Roofing Glossary of Terms

Abrasion Resistance – the ability to resist being worn away by contact with another moving, abrasive surface, such as foot traffic, mechanical equipment, wind-blown particles, etc.

Absorption – the ability of a material to accept within its body, quantities of gases or liquid, such as moisture.

Accelerated Weathering – the exposure of a specimen to a specified test environment for a specified time with the intent of producing in a shorter time period, effects similar to actual weathering.

Acid etch – in waterproofing, the use of a strong acid to remove the surface of concrete to expose the aggregate.

Acrylic coating – a liquid coating system based on an acrylic resin. Generally, a latex-based coating system that cures by air drying.

Acrylic resin – polymers of acrylic or methacrylic monomers. Often used as a latex base for coating systems.

Active metal (anodic) – a metal or material that readily gives up electrons to a cathodic (noble) material. (See anodic). An active metal will corrode in the presence of moisture when in contact with a cathodic metal.

Adhere – to cause two surfaces to be held together by adhesion, typically with asphalt or roofing cements in built-up roofing and with contact cements in some single-ply membranes.

Adhesion – steady or firm attachment.

Adhesive bond break – a material to facilitate independent movement between two units that would otherwise bond together.

Aged R-value – thermal resistance value established by utilizing artificial conditioning procedures for a prescribed time period.

Aggregate—(1) Crushed stone, crushed slag, or water-worn gravel used for surfacing a built-up roof; (2) Any granular mineral material.

Aging – the effect on materials that are exposed to an environment for an interval of time.

Air Leakage – the unintended movement of air from a location where it is intended to be contained to another location.

Alligatoring – Shrinkage cracking of the surfacing bitumen on a built-up roof, producing a pattern similar to an alligator’s hide. The cracks may or may not extend through the entire surfacing bitumen thickness.

Aluminized Steel – sheet steel with a thin aluminum coating bonded to the surface to enhance weathering characteristics.

Aluminum – a nonrusting, malleable metal sometimes used for metal roofing and flashing.

Alloys, polymeric – A blend of two or more polymers, e.g., a rubber and a plastic to improve a given property, e.g., impact strength.

Ambient Temperature – the temperature of the air; air temperature.

Anodic – a metal or material that readily gives up electrons to a cathodic material in the presence of a electrolyte (see Galvanic series).

Anticapillary hem – a hem used in a metal panel seam to reduce the potential for water migration.

Application Rate – the average quantity (mass, volume, or thickness) of material applied per unit area.

Apron Flashing – a term used for a flashing located at the juncture of the top of the sloped roof and a vertical wall, chimney or steeper-sloped roof.

Architectural panel – a metal roof panel, typically a double standing seam or batten seam; usually requires solid decking underneath and relies on slope to shed water.

Architectural shingle – an asphalt shingle that provides a dimensional appearance.

Area divider – a raised, flashed assembly typically a single- or double-wood member attached to a wood base plate, that is anchored to the roof deck. It is used to accommodate thermal stresses in a roof system where an expansion joint is not required, or to separate large roof areas or separate roof systems comprised of different/incompatible materials, and may be used to facilitate installation of tapered insulation.

Area practices – design or application techniques peculiar to a specific geographical region.

Asbestos – a group of natural, fibrous, impure silicate materials..

Asphalt – a dark brown or black substance found in a natural state or, more commonly, left as a residue after evaporating or otherwise processing crude oil or petroleum. Asphalt may be further refined to conform to various roofing grade specifications: Dead-Level Asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type I. Flat Asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type II. Steep Asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type III. Special Steep Asphalt: a roofing asphalt conforming to the requirements of ASTM Specification D 312, Type IV.

Asphalt emulsion – a mixture of asphalt particles and an emulsifying agent, such as bentonite clay and water.

Asphalt felt – An asphalt-saturated and/or asphalt-coated felt (see Felt).

Asphalt primer – see Primer.

Asphalt roof cement – a trowelable mixture of solvent-based bitumen, mineral stabilizers, other fibers and/or fillers. Classified by ASTM Standard D 2822-91 Asphalt Roof Cement, and D 4586-92 Asphalt Roof Cement, Asbestos-Free, Types I and II. Type I is sometimes referred to as “plastic cement,” and is made from asphalt characterized as self-sealing, adhesive and ductile, and conforming to ASTM Specification D 312, Type I; Specification D 449, Types I or II; or Specification D 946 (see Plastic cement and Flashing cement.) Type II is generally referred to as “vertical-grade flashing cement,” and is made from asphalt characterized by a high softening point and relatively low ductility, and conforming to the requirement of ASTM Specification D 312, Types II or III; or Specification D 449, Type III. (see Plastic cement and Flashing cement.)

Asphalt shingle – a shingle manufactured by coating a reinforcing material (felt or fibrous glass mat) with asphalt and having mineral granules on the side exposed to the weather. (see Shingle)

Asphalt, air blown – An asphalt produced by blowing air through molten asphalt at an elevated temperature to raise its softening point and modify other properties.

Asphaltene – a high molecular weight hydrocarbon fraction precipitated from asphalt by a designated solvent (paraffinic naphtha) at a specified temperature and solvent-asphalt ratio.

Atactic – A chain of molecules in which the position of the side methyl groups is more or less random. (Amorphic; Low Crystallinity)

Atactic polypropylene – a group of high molecular weight polymers formed by the polymerization of propylene.

Attic – the cavity or open space above the ceiling and immediately under the roof deck of a steep-sloped roof.

Back-nailing (also referred to as “Blind-nailing”) – the practice of blind nailing the back portion of a roofing ply, steep roofing unit, or other components in a manner so that the fasteners are covered by the next sequential ply, or course, and are not exposed to the weather in the finished roof system.

Back-Surfacing – fine mineral matter applied to the back side of asphalt shingles and roll roofing to keep them from sticking together while packaged.

Ballast – Loose aggregate, concrete pavers, or other material designed to prevent wind uplift or flotation of a loose-laid roof system.

Bar joist – (see Steel joist).

Barrel vault – a building profile featuring a rounded profile to the roof on the short axis, but with no angle change on a cut along the long axis.

Barrier board – noncombustible board stock material of low thermal conductivity placed between two elements of a roof assembly.

Base flashing (membrane base flashing) – plies or strips of roof membrane material used to close-off and/or seal a roof at the horizontal-to-vertical intersections, such as at a roof-to-wall juncture. Membrane base flashing covers the edge of the field membrane. (see Flashing.)

Base ply – the bottom or first ply in a built-up roof membrane when additional plies are to be subsequently installed.

Base sheet – an impregnated, saturated, or coated felt placed as the first ply in some low-slope roof systems.

Batten – (1) cap or cover; (2) in a metal roof, a metal closure set over, or covering the joint between, adjacent metal panels; (3) in a wood, a strip of wood usually set in or over the structural deck, used to elevate and/or attach a primary roof covering such as tile; (4) in a single ply membrane roof system, a narrow plastic, wood, or metal bar which is used to fasten or hold the roof membrane and/or base flashing in place.

Batten seam – a metal panel profile attached to and formed around a beveled wood or metal batten.

Beaufort scale – A scale in which the force of the wind is indicated by numbers from 0 to 12. No.7 is “near gale” at 52-61 km/h (32-38 m.p.h.). No. 9 is “strong gale” at 76-87 km/h (47-54 m.p.h.).

Bentonite – a porous clay formed by the decomposition of volcanic ash that swells 5 to 6 times its original volume in the presence of water.

Bermuda seam – a metal panel profile featuring a step-down profile that runs perpendicular to the slope of the roof.

Bi-Level Drain – see Dual-Level Drain.

Bird bath – random, inconsequential amounts of residual water on a roof membrane.

Bird Screen – wire mesh used to prevent birds from entering the building through ventilators, louvers, or other openings. (See Insect Screen.)

Bitumen—(1) A class of amorphous, black or dark colored, (solid, semisolid, or viscous) cementitious substances natural or manufactured, composed principally of high molecular weight hydrocarbons, soluble in carbon disulfide, and found in asphalts, tars, pitches, and asphaltites; (2) A generic term used to denote any material composed principally of bitumen; (3) In the roofing industry there are two basic bitumens: asphalt and coal-tar pitch. Before application they are either (a) heated to a liquid state, (b) dissolved in a solvent, or (c) emulsified.

Bitumen-Stop – see Envelope and Bleed Sheet.

Bituminous emulsion – A suspension of minute globules of bituminous material in water or in an aqueous solution.

Bituminous, adj. – Containing or treated with bitumen. Examples: bituminous concrete, bituminous felts and fabrics, bituminous pavement.

Blackberry (also referred to as “Blueberry” or “Tar-boil”) – a small bubble or blister in the flood coat of an aggregate-surfaced built-up roof membrane.

Blanket (batt) insulation – Fiberglass insulation in roll form, often installed between metal roof panels and the supporting purlins, or between ceiling joists.

Bleed-sheet – a sheet material used to prevent the migration of bitumen.

Bleeder strip – (see Rake-Starter).

Blind-nailing – the use of nails that are not exposed to the weather in the finished roofing system.

Blister – an enclosed pocket of air, which may be mixed with water or solvent vapor, trapped between impermeable layers of felt or membrane, or between the membrane and substrate.

Block or board thermal insulation – Rigid or semi-rigid thermal insulation preformed into rectangular units.

Blocking – sections of wood (which may be preservative treated) built into a roof assembly, usually attached above the deck and below the membrane or flashing, used to stiffen the deck around an opening, act as a stop for insulation, support a curb, or serve as a nailer for attachment of the membrane and/or flashing.

Blocking, wood – Treated wood members designed to help prevent movement of insulation.

Blowing agent – A compounding ingredient used to produce gas by chemical or thermal action, or both, in manufacture of hollow or cellular articles.

Blueberry – A small bubble or blister in the flood coating of a gravel-surfaced membrane.

Bodied solvent adhesive – An adhesive consisting of a solution of the membrane compound in solvent used in the seaming of membranes.

Bond – The adhesive and cohesive forces holding two roofing components in positive contact.

Bond, Chemical – adhesion between surfaces, usually of similar materials, resulting from a chemical reaction or cross-linking of polymer chains.

Bond, Mechanical – adhesion between surfaces resulting from interfacial forces or a physical interlocking.

Bonding Agent – a chemical substance applied to a suitable substrate to create bond between it and a succeeding layer.

Boot – (1) a covering made of flexible material, which may be preformed to a particular shape, used to exclude dust, dirt, moisture, etc., from around a penetration; (2) a flexible material used to form a closure, sometimes installed at inside and outside corners.

Brake – hand- or power-activated machinery used to bend metal.

Bridging – (1) when membrane or base flashing is unsupported at a juncture; (2) bridging in steep-slope roofing occurs when reroofing over standard-sized asphalt shingles with metric-sized asphalt shingles.

Breaking strain—% elongation at which a sheet or other tested component ruptures under tensile force.

Breaking stress – Stress (in force per linear or area units) at which sheet, or other tested component, ruptures under tensile force.

British thermal unit (BTU) – the heat energy required to raise the temperature of 1 pound of water one degree Fahrenheit (joule). For the metric equivalent, see Joule.

Broadcast – uniformly cast or distribute grandular or aggregate surfacing material.

Brooming – to improve the embedding of a ply or membrane by using a broom or squeegee to smooth it out and ensure contact with the adhesive under the ply or membrane.

Buckle – an upward, elongated displacement of a roof membrane frequently occurring over insulation or deck joints. A buckle may be an indication of movement within the roof assembly.

Btuh – Btu per hour.

Building code – Published regulations and ordinances established by a recognized agency describing design loads, procedures, and construction details for structures. Usually applying to designated political jurisdiction (city, county, state, etc.). Building codes control design, construction, and quality of materials, use and occupancy, location and maintenance of buildings and structures within the area for which the code was adopted. (See Model Codes)

Built-up roofing (BUR) – A continuous, semi-flexible membrane consisting of multiple plies of saturated felts, coated felts, fabrics or mats assembled in place with alternate layers of bitumen, and surfaced with mineral aggregate, bituminous material, a liquid-applied coating or a granule surfaced cap sheet.

Bull – Roofer’s term for flashing or plastic cement.

Bundle – an individual package of shakes or shingles.

Bun stock – large solid box-like structure formed during the production of polystyrene insulation; individual board stock pieces are then cut from the bun.

Bush Hammer – a hammer, originally a hand tool but now usually power driven, having a serrated face containing many pyramid-shaped points; used to provide a roughened surface on concrete.

Butt joint – a joint formed by adjacent, separate sections of material, such as where two neighboring pieces of insulation abut.

Button punch – a process of indenting two or more thicknesses of metal that are pressed against each other to prevent slippage between the metal.

Butyl – rubber-like material produced by polymerizing isobutylene.

Butyl coating – an elastomeric coating system derived from polymerized isobutylene. Butyl coatings are characterized by low water vapor permeability.

Butyl rubber – A synthetic elastomer rubber based on isobutylene and a minor amount of isoprene. It is vulcanizable and features low permeability to gases and water vapor and good resistance to aging, chemicals and weathering.

Butyl tape – a sealant tape sometimes used between metal roof panel seams and/or end laps; also used to seal other types of sheet metal joints, and in various sealant applications.

C-channel – a structural framing member.

Calender – (1) to press between rollers or plates in order to smooth and glaze or to thin into sheets; (2) a machine for calendering.

Calendering – a manufacturing process by which some polymeric membranes and other sheetings are produced.

Camber – a slight convexity, arching or curvature (as of a beam, roof deck or road).

Canopy – Any overhanging or projecting roof structure with the extreme end usually unsupported, typically over entrances or doors.

Cant – in SPF-based roofing, a beveling of foam at horizontal/vertical joints to increase strength and promote water run off.

Cant strip – A beveled strip used under flashings to modify the angle at the point where the roofing or waterproofing membrane meets any vertical element.

Cap flashing – (1) usually composed of metal, used to cover or shield the upper edges of the membrane base flashing wall flashing; (2) a flashing used to cover the top of various buildings components, such as parapets or columns. (See Flashing and Coping.)

Cap sheet – a sheet, often granule-surfaced, used as the top ply of some built-up or modified bitumen roof membranes and/or flashings.

Capacitance meter – a device used to locate moisture or wet materials within a roof system by measuring the ratio of the change to the potential difference between two conducting elements separated by a non-conductor.

Capillary action – (1) the action by which the surface of a liquid where it is in contact with a solid is elevated or depressed depending on the relative attraction of the molecules of the liquid for each other and for those of the solid; (2) the siphoning of liquid into a joint or void between two adjacent surfaces.

Catalyst – an ingredient that initiates a chemical reaction or increases the raate of a chemical reaction when combined with another chemical.

Cathodic – a metal or material that readily attracts electrons from an anodic material in the presence of an electrolyte (see Galvanic Series).

Caulk – A composition of vehicle and pigment, used at ambient temperatures for filling joints/sealing joins or junctures that remains elastic for an extended period of time after application.

Caulking – (1) the physical process of sealing a joint or juncture; (2) sealing and making weather-tight the joints, seams, or voids between adjacent surfaces by filling with a sealant.

Cavitation – the formation of a partial vacuum or cavity in a liquid.

Cavity Wall – an exterior wall usually of masonry, consisting of an outer and inner withe separated by a continuous air space, but connected together by wire or sheet-metal tiles.

CCF – 100 cubic feet.

Cellular glass insulation – a rigid closed-cell insulation board made from crushed glass and hydrogen sulfide gas.

Cementitious waterproofing – heavy cement-based compounds and various additives that are mixed and packaged for use in a dry form; the packaged mixture is then mixed with water and liquid bonding agents to a workable concrete-like consistency.

Centipoise – a unit of measure of absolute viscosity. (The viscosity of water is one centipoise. The lower the number, the less viscous the material.)

Centistoke – a unit of viscosity; the ratio of a liquid’s absolute viscosity to the density of that liquid.

CERL – Construction Engineering Research Laboratory.

Chalk – a powdery residue on the surface of a material.

Chalk line – a line made on the roof or other flat surface by snapping a taut string or

cord dusted with colored chalk.

Chalk resistance – A measurement of performance for paint systems; the ability to resist a dusty/chalky appearance over time.

Chalking – A powdery residue on the surface of a material resulting from degradation or migration of an ingredient, or both.

Channel flashing – in steep-slope roof construction, a type of flashing used at roof-to-wall junctures and other roof-to-vertical plan intersections where an internal gutter is needed to handle runoff. Commonly used with profile tile.

Chemical resistance – the ability to withstand contact with specified chemicals without a significant change in properties.

Chevron – a style of metal panel seaming/design.

Chimney – stone, masonry, prefabricated metal, or a wood framed structure, containing one or more flues, projecting through and above the roof.

Channel mopping – See Strip mopping under Mopping.

Chlorinated polyethylene (CPE) – a thermoplastic material, used for single-ply roof membranes, composed of high molecular weight polyethylene which has been chlorinated with a process that yields a flexible rubber-like material.

Chlorosulfonated polyethylene (CSPE or CSM) – probably best known by the DuPont trade name HypalonTM), a synthetic, rubber-like thermoset material, based on high molecular weight polyethylene with suphonyl chloride, usually formulated to produce a self-vulcanizing membrane. Classified by ASTM Standard D 5019.

Cladding – a material used as the exterior wall enclosure of a building.

Cleat – a continuous metal strip, or angled piece, used to secure metal components (also see Clip).

Clerestory – an upward extension of enclosed space created by carrying a setback vertical, wall (typically glazed) up and through the roof slope. Two intersecting shed roofs on different planes.

Clip – a non-continuous metal component or angle piece used to secure two or more metal components together. (see Cleat.)

Clipped gable – a gable cutback near the peak in a hip-roof form.

Closed-cut valley – a method of valley application in which shingles from one side of the valley extend across the valley while shingles from the other side are trimmed back approximately 2 inches (51 mm) from the valley centerline.

Closure strip – A resilient strip such as neoprene, flat on one side and formed to the contour of ribbed sheets on the other, used to close openings created by joining metal sheets and flashings.

Coal tar bitumen – a proprietary trade name for Type III coal tar used as the damp proofing or waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems, conforming to ASTM D 450, Type III.

Coefficient of thermal expansion – The change in length per unit of length for a unit change in temperature. (Thus the coefficient per 0F must be multiplied by 1.8 for the coefficient per oC.)

Coal tar – a dark brown to black colored, semi-solid hydrocarbon produced by the distillation of coal. Coal tar pitch is further refined to conform to the following roofing grade specifications:

Coal tar felt – A felt saturated or impregnated with refined coal tar.

Coal tar pitch – Dark brown to black, solid cementitious material obtained as residue in the partial evaporation or distillation of coal tar. A coal tar used as the waterproofing agent in dead-level or low-slope built-up roof membranes and membrane waterproofing systems, conforming to ASTM Specification D 450, Type I.

Coal tar roof cement – a trowelable mixture of processed coal tar base, solvents, mineral fillers and/or fibers. Classified by ASTM Standard D 4022, “Coal Tar Roof Cement, Asbestos Container.”

Coal tar waterproofing pitch – a coal tar used as the dampproofing or waterproofing agent in below-grade structures, conforming to ASTM Specification D 450, Type II.

Coarse orange peel surface texture – a surface showing a texture where nodules and valleys are approximately the same size and shape. This surface is acceptable for receiving a protective coating because of the roundness of the nodules and valleys.

Coated base sheet – a coated felt intended to be used as a base ply in a built-up or modified bitumen roof membrane.

Coated fabric – Fabrics impregnated and/or coated with a plastic like material in the form of a solution, dispersion hot melt, or powder. (The term also applies to materials resulting from the application of a preformed film to a fabric by means of calendering.)

Coated sheet (or felt)—(1) An asphalt felt that has been coated on both sides with harder, more viscous asphalt; (2) A glass fiber felt that has been simultaneously impregnated and coated with asphalt on both sides.

Coating – a layer of liquid material applied to a surface for protection or appearance.

Cobwebbing – a phenomenon observed during spray application characterized by the formation of web-like threads along with the usual droplets leaving the spray gun nozzle.

Code – a collection of laws (regulations, ordinances or statutory requirements) adopted by governmental authority. (see Building code and Model code.)

Coefficient of thermal expansion – the coefficient of change in dimension of a material per unit of dimension per degree change in temperature.

Cohesion – the molecular forces of attraction by which the body of a material is held together.

Coil coating – the application of a finish to a coil of metal using a continuous mechanical coating process.

Cold Flow – relatively slow deformation of a material at or below room temperature. (See Creep).

Cold forming – the process of shaping metal into desired profiles without the application of heat.

Cold roof assembly – a roof assembly configured with the insulation below the deck, not typically in contact with the deck, allowing for a ventilation space. The temperature of the roof assembly remains close to the outside air temperature.

Cold process roofing – a continuous, semi-flexible roof membrane, consisting of a ply or plies of felts, mats or other reinforcement fabrics that are laminated together with alternate layers of liquid-applied (usually asphalt-solvent based) roof cements or adhesives installed at ambient or a slightly elevated temperature.

Collector Box – see Conductor Head.

Color stability – the ability of a material to retain its original color after exposure to weather.

Column – in structures, a relatively long, slender structural compression member such as a post, pillar or strut; usually vertical which acts in (or near) the direction of its longitudinal axis.

Combing ridge – a term used to describe an installation of finishing slate or wood at the ridge of a roof whereby the slates on one side project beyond to the apex of the ridge.

Combustible – capable of burning.

Combustion – a chemical process of oxidation that occurs at a rate fast enough to produce heat and usually light either as glow or flames; the process of burning.

Compatible materials – two or more substances that can be mixed, blended, or attached without separating, reacting, or affecting the materials adversely.

Composite board roof insulation – rigid board insulation generally comprised of perlite or wood fiberboard factory bonded to polyisocyanurate or polystyrene.

Composition shingle – a unit of asphalt shingle roofing.

Compounded thermoplastics – a category of roofing membranes made by blending thermoplastic resins with plasticizers, various modifiers, stabilizers, flame retardants, UV absorbers, fungicides, and other proprietary substances, alloyed with proprietary organic polymers.

Compressive strength – the property of a material that relates to its ability to resist compression loads.

Concealed plate – see Cover plate.

Concealed-nail method – a method roofing application in which all nails are driven into the underlying course of roofing and covered by a subsequent, overlapping course.

Condensate – the liquid resulting from the condensation of a gas.

Condensation – The conversion of water vapor or other gas to liquid as the temperature drops or atmospheric pressure rises. (See also Dew Point)

Condense – to make denser or more compact, as when a material (e.g., water vapor) changes from its gas phase to its liquid phase.

Conditioning – the storage of a material specimen under specified temperature, humidity, etc. for a specified time prior to testing.

Conductance, thermal – The thermal transmission in unit time through unit area of a particular body or assembly having defined surfaces, when unit average temperature difference is established between the surfaces. C=(W/ m2•K) C=(Btu/h•ft2•0F).

Conductivity (Thermal) – The time rate of transfer of heat by conduction through a unit thickness across unit area for unit difference of temperature.

Conductivity, transmission, by conduction only, in unit time through unit area between two isothermal surfaces of an infinite slab of a homogeneous material of unit thickness, in a direction perpendicular to the surface, when unit temperature difference is established between the surfaces.

Conductor head – an enlargement or catch basin at the top of a downspout or leader to receive rainwater from a gutter or scupper.

Construction joint – (1) a joint where two successive placements of concrete meet; (2) a separation provided in a building which allows its component parts to move with respect to each other.

Contact cements – adhesives used to adhere or bond various roofing components. These adhesives adhere mated components immediately on contact of surfaces to which the adhesive has been applied.

Contamination – the process of making a material or surface unclean or unsuited for its intended purpose, usually by the addition or attachment of undesirable foreign substances.

Control joint – a groove which is formed, sawed, or tooled in a concrete or masonry structure to regulate the location and amount of cracking and separation resulting from the dimensional change or different parts of the structure, thereby avoiding the development of high stresses.

Coping – the covering piece on top of a wall exposed to the weather, usually made of metal, masonry, or stone and sloped to carry off water.

Copolymer – the product of polymerization of two or more substances (as two different isomers) together.

Copolymerization – a chemical reaction that results in the bonding of two or more dissimilar monomers to produce large, long-chain molecules that are copolymers.

Copper

a natural weathering metal used in metal roofing or flashing; typically used in 16 ounce per square foot (0.56 mm) and 20 ounce per square foot (0.69 mm) thicknesses.

Core cut or core sample – (1) a sample from a low-slope roof system taken for the purpose of obtaining primarily qualitative information about its construction. Typically, core cut analysis can verify or reveal the type of membrane surfacing; the type of membrane; the approximate number of plies; the type, thickness and condition of the insulation (if any); and the type of deck used as a substrate for the roof system. (2) for in SPF-based roof systems, core cuts are used to obtain both quantitative and qualitative information, such as the thickness of the foam, the thickness and adhesion of the coating, thickness of individual passes and adhesion between passes and the adhesion of the foam to its substrate.

Cornice – the decorative horizontal molding or projected roof overhang.

Counter batten – vertical wood strips installed on sloped roofs over which horizontal battens are secured. The primary roof covering is attached or secured to these horizontal battens.

Counterflashing – Formed metal or elastomeric sheeting secured on or into a wall, curb, pipe, rooftop unit, or other surface, to shield the upper edge of a base flashing and its associated fasteners.

Course – (1) the term used for a row of roofing material that forms the roofing, waterproofing or flashing system; (2) one layer of a series of materials applied to a surface (e.g., a five-course wall flashing is composed of three applications of roof cement with one ply of felt or fabric sandwiched between two layers of roof cement).

Cove – see Fillet.

Cover board – an insulation board used over closed cell plastic foam insulation (e.g., polyisocyanurate) to prevent blistering when used in conjunction with hot bituminous membranes. Suitable cover board insulation are glass-faced siliconized gypsum board, glass-fiber board, perlite board, wood-fiber board of mineral-fiber board. Cover boards are also recommended between polyisocyanurate insulation and single ply membranes to protect the polyisocyanurate.

Cover plate – a metal strip sometimes installed over or under the joint between formed metal pieces.

Coverage – The surface area to be continuously covered by a specific quantity of a particular material.

Covering – The exterior roof and wall covering for a metal building system.

CPA – copolymer alloy.

CPE – Chlorinated Polyethylene.

Crack – a non-linear separation or fracture occurring in a material.

Cream time – time in seconds (at a given temperature) when the A and B components of polyurethane foam will begin to expand after being mixed. Recognizable as a change in color of the materials.

Creep – the permanent deformation of a roofing material or roof system caused by movement of the roof membrane, or compression of a roof insulation board at fastener positions, that results from continuous load or thermal stress or loading. Creep at roof temperature is sometimes called “cold flow.”

Cricket – A relatively small, elevated area of a roof constructed to divert water from a horizontal intersection of the roof with a chimney, wall, expansion joint or other projection. (See Saddle)

Cross Ventilation – the effect that is provided when air moves through a roof cavity between the vents.

Cross-linking – the formation of chemical bonds between polymeric chains. Cross-linking of rubber is referred to as vulcanizing or “curing.”

CRREL – Cold Regions Research and Engineering Laboratory.

Crystalline waterproofing – a compound of cement, quartz or silica sand, and other active chemicals that are mixed and packaged for use in a dry powder form; the packaged mixture is then mixed with water and applied to a concrete surface where it penetrates into the pores of concrete.

CSI – Construction Specifications Institute

CSM – ASTM designation for chlorosulfonated polyethylene. (See CSPE.)

CSPE – chlorosulfonated polyethylene.

Cupola – a relatively small roofed structure, generally set on the ridge or peak of a main roof area for ventilation or aesthetic purposes.

Curb – (1) a raised member used to support roof penetrations, such as skylights, mechanical equipment, hatches, etc. above the level of the roof surface; (2) a raised roof perimeter relatively low in height.

Cure – To change the properties of a polymeric system into a more stable, usable condition by the use of heat, radiation, or reaction with thermal

Cure time – the time required for a material to reach its desirable long-term physical characteristics.

Cured concrete – concrete that has attained its intended design performance properties.

Curing agent – an additive in a coating or adhesive that results in increased chemical activity between the components with an increase or decrease in rate of cure.

Curing compound – a liquid that is sprayed or otherwise applied to newly placed concrete which retards the loss of water during curing.

Cutback – Solvent-thinned bitumen used in cold process roofing adhesives, flashing cements, and roof coatings.

Cutoff – a permanent detail designed to prevent lateral water movement in an insulation system and used to isolate sections of a roofing system. (Note: A cutoff is different from a tie-in, which may be a temporary or permanent seal.) (see Tie-In.)

Cutout – the open portions of a strip shingle between the tabs. Sometimes referred to as a keyway.

Dampproofing – Treatment of a surface or structure to resist the passage of water in the absence of hydrostatic pressure.

Dead-level – Absolutely horizontal, or zero slope. (See Slope)

Dead loads – the weight of a structure itself, including the weight of fixtures or equipment permanently attached to it.

Dead level asphalt – see Asphalt.

Deck – a structural component of the roof of a building. The deck must be capable of safely supporting the design dead and live loads, including the weight of the roof systems, and the additional live loads required by the governing building codes and provide the substrate to which the roofing or waterproofing system is applied the structural surface of a building to which a roof assembly is installed. Decks are either non-combustible (e.g., corrugated metal, concrete, or gypsum) or combustible (e.g., wood plank or plywood).

Deflection (bowing, sagging) – (1) the deformation of a structural member as a result of loads acting on it; (2) any displacement in a body from its static position, or from an established direction or plane, as a result of forces acting on the body.

Degradation – a deleterious change in the chemical structure, physical properties or appearance of a material from natural or artifical exposure (e.g., exposure to radiation, moisture, heat, freezing, wind, ozone, oxygen, etc.)

Degree-days – a unit used in estimating the fuel consumption for a building; equal to the number of degrees that the mean temperature, for a 24-hour day, is below the “base temperature”; the base temperature is taken as 65 degrees F (18.3 C) in the U.S.A.

Delamination – Separation of the plies in a membrane or separation of insulation layers after lamination.

Depth of measurement – The maximum thickness of a roof system upon which a given moisture survey method is effective.

Design loads – The “live load” (i.e. super- imposed loads) that a structure is designed to resist (with appropriate safety factor) plus “dead load” (i.e., weight of permanent loads).

Dew point – The temperature at which water vapor starts to condense in cooling air at the existing atmospheric pressure and vapor content.

Dew-point temperature – the temperature at which air becomes saturated with water vapor. The temperature at which air has a relative humidity of 100%.

Diaphragm – a floor slab, metal wall panel, roof panel, or the like, having a sufficiently large in-plane shear stiffness and sufficient strength to transmit horizontal forces to resisting systems.

Diffusion – the movement of water vapor from regions of high concentration (high water vapor pressure) toward regions of lower concentration.

Dimensional shingle – a shingle that is textured, overlayed, or laminated and designed to produce a three-dimensional effect. (also see Laminated shingle and Architectural shingles.)

Dimensional stability – the degree to which a material maintains its original dimensions when subjected to changes in temperature and humidity.

Dome – a roof that is shaped like a half-circle, or a variation of one.

Dormer – a structure projecting from a sloping roof usually housing a window or ventilating louver.

Double coverage – application of asphalt, slate, or wood roofing such that the lapped portion is at least 2 inches (50 mm) wider than the exposed portion, resulting in two layers of roofing material over the deck.

Double Graveling – the process of applying two layers or flood coats of bitumen and aggregate to a built-up roof. Loose aggregate should be swept from the first application prior to the second coating of bitumen and aggregate. Approximately 50% of the second aggregate application will remain adhered in the bitumen flood coat unless physically removed.

Double lock standing seam – in a metal roof panel or metal cap, a standing seam that uses a double overlapping interlock between two metal panels. (see Standing seam.)

Double pour – Doubling of flood-coat, graveling- in operation, to provide additional waterproofing integrity for a BUR membrane.

Downspout – a vertical pipe or conduit used to carry runoff water from a scupper, conductor head or gutter of a building to a lower roof level or to the ground or storm water runoff system.

Drag load – the external force (e.g., from the weight of ice and snow) applied to a steep-slope roof system component forcing the component down slope.

Drain – an outlet or other device used to collect and direct the flow of runoff water from a roof area.

Drip edge – a metal flashing or other overhanging component with an outward projecting lower edge, intended to control the direction of dripping water and help protect underlying building components.

Dry bulb temperature – the temperature of air as measured by an ordinary thermometer.

Dry film thickness – the thickness, expressed in mils, of an applied and cured coating or mastic. For comparison, see Wet film thickness.

Dry-In or Dry-In Felt – usually the underlayment or the process of applying the underlayment for steep roofing.

Drying time – the time required for the loss of volatile components so that the material will no longer be adversely affected by weather conditions such as dew, rain, or freezing.

Dual level drain – in waterproofing, an outlet or other device with provisions for drainage at both the wearing surface level and the waterproofing membrane levels used to collect and direct the flow of runoff water from a horizontal slab.

Durability – the ability to withstand physical, chemical, or environmental abuse.

Dust Free – a surface is considered dust free when a finger can be lightly run over the surface without picking up any dirt, dust, or chalk on the finger.

Dynamic load – any load which is nonstatic, such as a wind load or a moving live load.

Eave – The line along the sidewall formed by the intersection of the planes of the roof and wall.

Eave height – The vertical dimension from finished floor to the eave.

Eaves-trough – see Gutter.

ECH – polyepichlorohydrin, commonly referred to as epichlorohydrin. (see Epichlorohydrin.)

Edge stripping – membrane flashing strips cut to specific widths used to seal/flash perimeter edge metal and the roof membrane application of felt strips cut to narrower widths than the normal felt-roll width to cover a joint between metal perimeter flashing and built-up roofing.

Edge venting – The practice of providing regularly spaced protected openings at a roof perimeter to relieve water vapor pressure in the insulation. (It is of doubtful efficacy.)

Efflorescence – A deposit or encrustation of soluble salts, generally white and most commonly consisting of calcium sulfate, that may form on the surface of stone, brick, concrete, or mortar when moisture moves through and evaporates on the masonry. caused by free alkalies leached from mortar, grout, or adjacent concrete.

EIP – ethylene interpolymer.

Elasticity – the property of a body that causes it to tend to return to its original shape after deformation (as stretching, compression or torsion).

Elastomer – A macromolecular material that returns rapidly to its approximate initial dimensions and shape after subsequent release of stress.

Elastomeric – the elastic, rubber-like properties of a material that will stretch when pulled and will return relatively quickly to its original shape when released.

Elastomeric coating – a coating that is capable of being stretched at least twice its original length (100 percent elongation) and recovering to its original dimensions.

Electrolyte – a liquid, most often a solution, that will conduct current.

Elongation – the ratio of the extension of a material to the length of the material prior to stretching.

Embedment—(1) the process of pressing a felt, aggregate, fabric, mat, or panel uniformly and completely into hot bitumen or adhesive to ensure intimate contact at all points; (2) the process of pressing granules into coating in the manufacture of factory prepared roofing, such as shingles.

Embrittlement – the loss of flexibility or elasticity of a material.

Emulsion – a mixture of bitumen and water, with uniform dispersion of the bitumen or water globules, usually stabilized by an emulsifying agent or system.

End lap – the distance of overlap where one ply, pane, or piece extends beyond the end of the immediately adjacent underlying ply, panel, or piece.

Envelope (Bitumen-stop) – a continuous membrane edge seal formed at the perimeter and at penetrations by folding the base sheet or ply over the plies above and securing it to the top of the membrane. The envelope prevents bitumen seepage from the edge of the membrane.

EPDM – A synthetic elastomer based on ethylene, propylene, and a small amount of a non-conjugated diene to provide sites for vulcanization. EPDM features excellent heat, ozone and weathering resistance, and low temperature flexibility.

Epichlorohydrin (ECH) – a synthetic rubber including two epichlorohydrin based elastomers. It is similar to and compatible with EPDM.

Epoxy – a class of synthetic, thermosetting resins that produce tough, hard, chemical-resistant coatings and adhesives.

Equilibrium moisture content (EMC) – (1) the moisture content of a material stabilized at a given temperature and relative humidity, expressed as percent moisture by weight.

Equiviscous temperature (EVT) – application range

the recommended bitumen application temperature range. The range is approximately 25 degrees F (14 degrees C) above or below the EVT, thus giving a range of approximately 50 degrees F (28 degrees C). The EVT range temperature is measured in the mop cart or mechanical spreader just prior to application of the bitumen to the substrate.

Equiviscous temperature (EVT) for asphalt – the recommended EVT for roofing asphalt (ASTM D 312, Type I, II, III, or IV) is as follows Mop Application: the temperature at which the asphalt’s apparent viscosity is 125 centipoise (0.125 Pa s). Mechanical Spreader Application: the temperature at which the asphalt’s apparent viscosity is 75 centipoise (0.075 Pa s). Note: In order to avoid the use of two kettles if there are simultaneous mop and mechanical spreader applications, the EVT for mechanical spreader application can be used for both application techniques.

Equiviscous temperature (EVT) for coal tar – the recommended EVT for roofing coal tar (ASTM D 450, Type I or III) is the temperature at which the coal tar’s apparent viscosity is 25 centipoise (0.025 Pa s).

Ethylene interpolymers (EIP) – a group of thermoplastic compounds generally based on PVC polymers from which certain single-ply roofing membranes can be formulated.

Ethylene propylene diene terpolymer (EPDM) – designated nomenclature of ASTM for a terpolymer of ethylene, propylene, and a diene. EPDM material is a thermosetting synthetic elastomer.

EVT – Equiviscous temperature.

Exhaust ventilation – air that is vented or exhausted from the roof cavity, typically through vents installed on the up slope portion of the roof. For example, with most steep-slope roof assemblies, exhaust vents are typically located at or near the ridge.

Exotherm – Heat generated in a chemical reaction.

Expansion cleat – a cleat designed to accommodate thermal movement of the metal roof panels.

Expansion joint – A structural separation between two building elements that allows free movement (expansion or contraction) between elements without damage to the roofing or waterproofing system.

Exposure—(1) (1) the traverse dimension of a roofing element or component not overlapped by an adjacent element or component in a roof covering. For example, the exposure of any ply in a built-up roof membrane may be computed by dividing the felt width, minus 2 inches (51 mm), by the number of shingled plies; thus, the exposure of 36 inch (914 mm) wide felt in a shingled, four-ply membrane should be approximately 81/2 inches (216 mm); (2) the dimension of sidewall or roofing covering that is not covered or overlapped by the up slope course of component. The typical exposure for a standard-size, 3-tab shingle is 5 inches (127 mm), depending upon manufacturer specifications.

Extrusion – a process in which heated or unheated material is forced through a shaping orifice (a die) in one continuously formed shape, as in film, sheet, rod or tubing.

Eyebrow – a dormer, usually of small size, whose roof line over the upright face is typically an arched curve, turning into a reverse curve to meet the horizontal at either end. Also, a small shed roof projecting from the gable end of the larger, main roof area.

Fabric – a woven cloth or material of organic or inorganic filaments, threads, or yarns used for reinforcement in certain membranes and flashings.

Fabric reinforcement – A fabric, scrim, etc., used to add structural strength to a 2 or more ply polymeric sheet. Such sheeting is referred to as “supported”.

Fabrication—(1) The manufacturing process performed in a plant to convert raw material into finished metal building components. The main operations are cold-forming, cutting, punching, welding, cleaning, and painting; (2) the creation of large panels of rubber from smaller calendar width sheets as in EPDM.

Factory Mutual Research (FMR) – commonly referred to as “FM,” a research and testing organization that classifies roofing components and assemblies for their fire, traffic, impact (hail), weathering, and wind-uplift resistance for four major insurance companies in the United States.

Factory seam – a splice/seam made by the manufacturer during the assembly of sections of materials into larger sheets/panels.

Fading – any lightening of initial color.

Fallback – a reduction in the softening point, sometimes caused by refluxing or overheating in a relatively closed container. (see Softening Point Drift.)

Fascia – (1) in steep-slope roofing, a board that is nailed to the ends of a roof rafter; sometimes supports a gutter; (2) in a low-slope roofing, the vertical or steeply sloped roof or trim located at the perimeter of a building. Typically, it is a border for the low-slope roof system.

Fastener – any of a wide variety of mechanical securement devices and assemblies, including nails, staples, screws, cleats, clips, and bolts, which may be used to secure various components of a roof assembly.

Feathering strips – tapered wood filler strips placed along the butt ends of old wood shingles to create a relatively smooth surface when reroofing over existing wood shingle roofs. Referred to in some regions of the country as “horse feathers” or leveling strips.

Felt machine (Felt Layer) – a mechanical device used for applying bitumen and roofing felt or ply sheet simultaneously.

Felt – A flexible sheet manufactured by the interlocking of fibers through a combination of mechanical work, moisture, and heat, without spinning, weaving, or knitting. Roofing felts are manufactured from vegetable fibers (organic felts), glass fibers (glass fiber felts) or polyester fibers (synthetic fiber mats).

Ferrule – a metal sleeve placed inside a gutter at the top. A spike or screw is nailed/screwed through the gutter face and ferrule into the fascia board to hold the gutter in place. The ferrule acts as a spacer in the gutter to maintain its original shape.

Fiberglass Insulation – blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls. Rigid boards usually have an asphalt and kraft paper facer.

Field of the Roof – the central or main portion of a roof, excluding the perimeter and flashing.

Field seam – a splice or seam made in the field (not factory) where overlapping sheets are joined together using an adhesive, splicing tape, or heat- or solvent-welding.

Filler – a relatively inert ingredient added to modify physical characteristics.

Fillet – a heavy bead of waterproofing compound or sealant material generally installed at the point where vertical and horizontal surfaces meet; the desired effect to take out the 90 degree angle at the base of a vertical flashing.

Film – sheeting having a nominal thickness not greater than 10 mils (0.25 mm).

Film thickness – the thickness of a membrane or coating. Wet film thickness is the thickness of a coating as applied; dry film thickness is the thickness after curing. Film thickness is usually expressed in mils (thousandths of an inch).

Fin – a term used to describe a deck surface condition. A sharp raised edge (generally in concrete) capable of damaging a roof membrane or vapor retarder.

Fine mineral surfacing – water-insoluble, inorganic material, more than 50 percent of which passes through a No. 35 sieve. Used on the surface of various roofing materials and membranes to prevent sticking.

Fire resistance – the property of a material or assembly to withstand fire or give protection from it.

Fire retardant treated (FRT) plywood – plywood which has been impregnated, under pressure, with mineral salts; in the event of fire, the burning wood and salts emit noncombustible gases and water vapor instead of the usual flammable vapors.

Fishmouth-(also referred to as an edge wrinkle) (1) a half-cylindrical or half-conical shaped opening or void in a lapped edge or seam, usually caused by wrinkling or shifting of ply sheets during installation; (2) in shingles, a half-conical opening formed at a cut edge.

Flaking – in protective coatings, the detachment of small pieces of the coating film.

Flame retardant – a chemical used to impart flame resistance.

Flame spread – a propagation of a flame away from its source of ignition.

Flammability – those characteristics of a material that pertain to its relative ease of ignition and ability to sustain combustion.

Flange – the projecting edge of a rigid or semi-rigid component, such as a metal edge flashing flange.

Flash point – the lowest temperature at which vapors above a volatile combustible substance ignite in air when exposed to a flame.

Flashing – components used to weatherproof or seal the roof system edges at perimeters, penetrations, walls, expansion joints, valley, drains, and other places where the roof covering is interrupted or terminated. For example, membrane base flashing covers the edge of the field membrane, and cap flashings or counterflashings shield the upper edges of the base flashing.

Flashing cement – a trowelable mixture of solvent-based bitumen and mineral stabilizers that may include asbestos or other inorganic or organic fibers. Generally, flashing cement is characterized as vertical-grade, which indicate it is intended for use on vertical surfaces. (see Asphalt Roof Cement and Plastic Cement.)

Flashing collar – (sometimes referred to as a roof jack or flashing boot) an accessory flashing used to cover and/or seal soil pipe vents and other penetrations through the roof.

Flash point – Temperature at which a test flame ignites vapor above a liquid surface.

Flat asphalt – A roofing asphalt conforming to the requirements of Specification D312, Type II.

Flat lock – a method of interlocking metal panels in which one panel edge is folded back on top of itself and the other panel is folded under, after which the two panels are hooked together.

Fleece – mats or felts composed of fibers, sometimes used as a membrane backer.

Flood (pour) coat – the surfacing layer of bitumen into which surfacing aggregate is embedded on an aggregate-surfaced built-up roof.

Flood test – the procedure where a controlled amount of water is temporarily retained over a horizontal surface to determine the effectiveness of the waterproofing system.

Fluid-applied elastomer – An elastomeric material, fluid at ambient temperature, that dries or cures after application to form a continuous membrane. Such systems normally do not incorporate reinforcement.

Fly-in – method of application for roll materials by which the dry sheet is set into the bitumen or adhesive applied to the roof surface.

FM – see Factory Mutual Research (FMR).

Foam stop – the roof edge treatment upon which SPF is terminated.

Force – a strength or energy exerted or brought to bear; cause of motion or change.

FPL – Forest Products Laboratory.

Framed Opening – an opening in a wall or roof of a building, surrounded by structural framing, usually for field installed accessories such as skylights or ventilators.

Froth pack – a term used to describe small, disposable aerosol cans that contain SPF components. Two component froth packs are available to do small repairs for sprayed polyurethane foam-based roofs.

Friability – The tendency of a material or product to crumble or break into small pieces easily.

G-90 – a designation for galvanized metal sheet, indicating 0.90 ounces (26 g) of zinc per square foot, measured on both sides.

Gable roof – A single-ridged roof that terminates in gable end(s).

Galvalume – trade name for a metal alloy coating that is composed of aluminum, zinc and silicone.

Galvanic action – an electrochemical action that generates electrical current between two metals of dissimilar electrode potential.

Galvanic series – an list of metals and alloys arranged according to their relative electrolytic potentials in a given environment.

Galvanize – to coat steel or iorn with zinc.

Galvanized steel – Steel coated with zinc for corrosion resistance.

Gambrel – a roof that has two pitches on each side, where the upper roof area has less slope than the lower roof areas.

Gauge – a metal thickness measurement.

Geocomposite – a prefabricated water drainage material used to relieve hydrostatic pressure against waterproofing and promote drainage.

Geodesic Dome – a rounded structure made of short, straight, triangular sections that form polygons.

Geotextile – a tightly woven fabric used to restrict the flow of fine soil particles and other contaminants while allowing water to pass freely through; used to protect drainage systems from clogging.

Girt – a horizontal beam that supports wall cladding between columns.

Glass felt – Glass fibers bonded into a sheet with resin and suitable for impregnation in the manufacture of bituminous waterproofing, roofing membranes, and shingles.

Glass fiber insulation – blanket or rigid board insulation, composed of glass fibers bound together with a binder, faced or unfaced, used to insulate roofs and walls.

Glass mat – A thin mat of glass fibers with or without a binder.

Glass transition – The reversible change in an amorphous polymer or in amorphous regions of a partially crystalline polymer from (or to) a viscous or rubbery condition to (or from) a hard and relatively brittle one.

Glaze coat—(1) The top layer of asphalt in a smooth surfaced built-up roof assembly; (2) A thin protective coating of bitumen applied to the lower plies or top ply of a built-up membrane, when application of additional felts, or the flood coat and aggregate surfacing are delayed.

Gloss – the shine, sheen, or luster of a dried film.

Grain – a unit used to measure in the English System of units; 7,000 grains equals 1 lb.; used as a measure of the weight of moisture in air.

Granule – (also referred to as mineral or ceramic granule) opaque, natural, or synthetically colored aggregate commonly used to surface cap sheets, shingles, and other granule-surfaced roof coverings.

Gravel – Coarse, granular aggregate, with pieces larger than sand grains, resulting from the natural erosion of rock.

Gravel stop – Flanged device, usually metallic, designed to prevent loose aggregate from washing off the roof and to provide a continuous finished edge for the roofing.

Groundwater level – at a particular site, the level below which the subsoil and rock masses of the earth are fully saturated with water.

Green building technology – Utilizing technology to reduce impact on the earth. Includes recyclability, reduction in carbon dioxide, ozone or other atmospheric pollutants, and reduction of urban heat islands.

Grout (Non-Shrink) – a cementitious material used to fill pitch-pans/pockets, prior to the application of a pourable sealer.

Gusset – used at the bottom of a steep-slope roof system valley, a large flat metal piece(s) wider than the valley to help prevent build-up at the base of the valley, either from debris or ice dam formations.

Gutter – a channeled component installed along the downslope perimeter of a roof to convey runoff water from the roof to the drain leaders or downspouts.

Gypsum board panels – cementititious board stock with noncombustible core primarily comprised of gypsum that is commonly used as a barrier board thermal barrier or cover board in a roof assembly.

Hand-tabbing – method of spot applying asphalt-based adhesive to shingles for securement and wind resistance.

Hardness – the relative resistance of a material to indentation.

Header – A horizontal framing structural member of a door, window, or other framed opening.

Headlap – the distance of overlap measured from the uppermost ply or course to the point where it laps over the undermost ply or course.

Heat Aging – controlled exposure of materials to elevated temperatures over time.

Heat flow – the quantity of heat transferred to or from a system in a unit of time.

Heat seaming – the process of joining thermoplastic films, membranes, or sheets by heating and then applying pressure to bring both materials in contact with each other. (see Heat welding.)

Heat transfer – The transmission of thermal energy from a location of higher temperature to a location of lower temperature. This can occur by conduction, convection or radiation.

Heat welding – method of melting and fusing together the overlapping edges of separate sheets or sections of polymer modified bitumen, thermoplastics or some uncured thermoset roofing membranes by the application of heat (in the form of hot air or open flame) and pressure. (see Heat seaming.)

Hem – the edge created by folding metal back on itself.

Hip – the inclined external angle formed by the intersection of two sloping roof planes.

Hip roof – A roof which rises by inclined planes from all four sides on the building. The line where two adjacent sloping sides of a roof meet is called the Hip.

Hoist – a mechanical lifting device.

Holiday – An area where a liquid applied material is missing, a void.

Honeycomb – voids left in concrete resulting from failure of the mortar to effectively fill the spaces among course aggregate particles.

Hot-dip metallic coating – Adherent protective coating applied by immersing steel in a molten bath of coating material.

Hood – Cover, usually light gage metal, over piping or other rooftop equipment.

“Hot stuff” or “hot” – A roofer’s term for hot bitumen.

Hue – the subjective perception of color such as red, yellow, green, blue, purple or some combination; white, black or gray possess no hue.

Humidity – The amount of moisture contained in the atmosphere. Generally expressed percent relative humidity. (The ratio of the vapor pressure to the saturation pressure for given conditions times 100.)

Humidity test – A test involving exposure of specimens at controlled levels of humidity and temperature.

HVAC – heating, ventilating, and air conditioning equipment.

Hybrid roof covering – combination of two or more separate and distinct roof membranes; e.g., three ply smooth BUR and a modified bitumen cap.

Hydration – the chemical reaction by which a substance (such as Portland cement) combines with water, giving off heat to form a crystalline structure in its setting and hardening.

Hydrocarbons – An organic chemical compound containing mainly the elements carbon and hydrogen. Aliphatic hydrocarbons are straight chain compounds of carbon and hydrogen. Aromatic hydrocarbons are carbon-hydrogen compounds based on the cyclic or benzene ring. They may be gaseous (CH4, ethylene, butadiene), liquid (hexene, benzene), or solid (Natural rubber, napthalene, cispolybutadiene).

Hydrostatic pressure relief system – a system of perimeter and/or under slab drains used to regulate the hydrostatic pressure in the earth surrounding a below-grade structure.

Hydrostatic pressure – the pressure equivalent to that exerted on a surface by a column of water of a given height.

Hygroscopic – attracting, absorbing and retaining atmosphere moisture.

HypalonTM – a registered trademark of E.I. duPont de Nemours & Co., for “chlorosulfonated polyethylene” (CSPE). (see Chlorosulfonated polyethylene.)

Ice dam – a mass of ice formed at the transition from a warm to a cold roof surface, frequently formed by refreezing melt-water at the overhang of a steep roof, causing ice and water to back up under roofing materials.

Ice dam protection membrane – a continuous membrane installed under steep slope roofing materials in areas subject to ice damming that prohibits water which gets through the roof covering from getting into the structure. Must also seal the fasteners that penetrates it.

Ignition temperature – the lowest temperature at which combustion will occur spontaneously under specific conditions.

Impact resistance – resistance to fracture under the sudden application of an exerted force.

Impregnate – in roofing materials manufacture, to completely surround the fibers in a felt or mat with bitumen, with the spaces between the fibers partially or completely filled without a continuous coating of bitumen on the surface.

In-service R-value – thermal resistance value established under installed conditions and measured over the expected service life of the material.

Incline – The slope of a roof expressed in percent or in the number of vertical units of rise per horizontal unit of run. (See Slope)

Infrared thermography – the process of displaying variations of apparent temperatures (variation of temperature or emissivity or both) over the surface of an object by measuring variations in infrared radiance.

Inorganic, adj – being or composed of materials other than hydrocarbons and their derivatives, or matter that is not of plant or animal origin.

Insect screen – wire mesh used to prevent insects from entering the building through ventilators, louvers, or other openings.

Insulation

any of a variety of materials designed to reduce the flow of heat, either from or into a building. (see also Thermal insulation.)

Internal pressure – Pressure inside a building, a function of wind velocity, building height, and number and location of openings.

lsocyanate – A highly reactive chemical grouping composed of a nitrogen atom bonded to a carbon atom bonded to an oxygen atom; =N=C=O; a chemical compound, usually organic, containing one or more isocyanate groups.

Isoboard – Abridgement of polyisocyanurate foam insulation board.

Joist — Any of the small timbers or metal beams arranged parallel from wall to wall to support a floor, ceiling or roof of a building.

Joist – any of the small timbers, metal or wood beams arranged parallel to each other and spanning from wall to wall to support a floor, ceiling, or roof of a building.

Joule – a unit of energy or work; equals the work done by a force of 1 newton which acts over a distance of 1 meter in the direction of the force.

k or k-Value – thermal conductivity; the time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient. In English (inch-pound) units of measurement, it is the number of BTUS that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in 1 hour with a temperature difference between the two surfaces of 1 degree F. It is expressed as Btu.inch/h.ft2.degrees F.

k-factor – thermal conductivity for a unit thickness of material. Expressed at BtuòIn/HròFt2ò_F. R-value is equal to the thickness of the thermal material divided by the k-factor (R=x/k where x = thickness).

Kerf – (1) a slit or notch made by a saw or cutting torch; (2) the width of a cut made by a saw or cutting torch.

Kesternich test – simulates acid rain conditions by subjecting test specimens to a sulfur dioxide atmosphere as well as condensing moisture for the purpose of evaluating rust/corrosion characteristics.

Knee cap – a metal cover trim that fits over a panel rib after it has been cut and bent.

Knuckle – a metal closure, either shop-or pre-fabricated, installed over the cut seam of a continuous metal roof panel at the transition from a steep-slope roof to a vertical roof or wall.

Kick-out (Elbow)—(Turn-Out) A lower downspout section used to direct water away from a wall.

Laitance – a weak layer of cement and aggregate fines on a concrete surface that is usually caused by an overwet mixture, overworking the mixture, improper or excessive finishing or combination thereof.

Laminate – to join layers of materials together using fusion; the process of joining layers of materials together using adhesion.

Laminated shingles – see Dimensional shingles or Architectural shingles.

Lap – that part of a roofing, waterproofing, or flashing component that overlaps or covers any portion of the same or another type of adjacent component.

Lap cement – an asphalt-based roof cement formulated to adhere overlapping plies or asphalt roll roofing.

Lapped joint – A joint made by placing one surface to be joined partly over another surface and bonding the overlapping portions.

Latex – a stable dispersion of polymeric substance in an essentially aqueous medium.

Layer (Plywood) – A layer is a single veneer ply or two or more plies laminated with parallel grain

Lead – a soft malleable, heavy metal; has low melting point and a high coefficient of thermal expansion.

Leader head – see Conductor head.

Leeward – the opposite direction from which the wind is blowing. The side sheltered from the wind.

Life Cycling Costing – a method of economic analysis that takes into account expected costs over the useful life of an asset.

Lift – the sprayed polyurethane foam that results from a pass. It usually is associated with a certain pass thickness and has a bottom layer, center mass and top skin in its makeup.

Live load – Live load means all loads including snow, exerted on a roof except dead, wind, and lateral loads.

Loose-laid membrane – A un-adhered roofing membrane anchored to the substrate only at the edges and penetrations through the roof and ballasted against wind uplift by loose aggregate or payers.

Mansard – a decorative steep-sloped roof on the perimeter of a building.

Mansard roof – a steeper roof that terminates into a flat roof at its high point.

Masonry – construction, usually set in mortar, of natural building stone or manufactured units, such as brick, concrete block, adobe, glass block, tile, manufactured stone or gypsum block.

Mastic – a thick adhesive material used as a cementing agent for holding waterproofing membrane in place. (see Asphalt roof cement).

Mat – a thin layer of woven, non-woven, or knitted fiber that serves as reinforcement to the material or membrane.

Mat slab – a concrete slab designed with reinforcement to resist the uplift forces created by hydrostatic pressure.

Material safety data sheets (MSDS) – a written description of the chemicals in a product and other pertinent data including such things as safe handling and emergency procedures. In accordance with OSHA regulations, it is the manufacturer’s responsibility to produce an MSDS and the employer’s responsibility to communicate its contents to employees.

MBDA – formerly Metal Builders Dealers Association, now Systems Builders Association.

MBMA – Metal Building Manufacturers Association

MCA – Metal Construction Association

Mechanical damage – in SPF-based roofing, physical damage to a completed SPF-based roof system not caused by normal wear and tear.

Mechanically-fastened membranes – generally used to describe membranes that have been attached at defined intervals to the substrate.

Membrane – A flexible or semi-flexible roof covering or waterproofing whose primary function is the exclusion of water.

Memory – Tendency of a material to regain a previous configuration—notably, the tendency of glass-fiber felts not to lie flat on their substrate after unrolling; the retraction of single-ply roll goods which were stretched during production or winding.

Metal – any of various opaque, fusible, ductile and typically lustrous substances that are good conductors of electricity and heat.

Metal Flashing – accessory components fabricated from sheet metal and used to weatherproof terminating roof covering edges. Frequently used as through-wall flashing, cap flashing (coping), counterflashing, step-flashing, etc. (See Flashing.)

Metal Film – a layer of foil made from a single metallic substance, or from an alloy, that is laminated to a membrane during manufacture. The metal foil serves as the weathering surface of the membrane or flashing material.

Metal rain collar – a metal counterflashing used to wrap a penetration and prevent water infiltration though the top of the penetration base flashing.

Metal roof panel – an interlocking metal sheet having a minimum installed weather exposure of 3 square feet (279000 mm2 or 0.28 m2)per sheet.

Metal roof shingle – an interlocking metal sheet having an installed weather exposure less than 3 square feet (279000 mm2 or 0.28 m2) per sheet.

Metallic waterproofing – consist of finely graded iron particles combined with an oxidizing catalyst. When mixed with water (or water, cement, and sand), the finely distributed particles expand, creating a waterproof layer that becomes a part of the surface to which it is applied.

Meter – unit of length measurement in the metric system, 1 meter is equal to 39.37 inches.

Mica Dust – crystallized complex silicate minerals that are pulverized into dust form for use as a release agent. (See Talc.)

Microbiological Resistance – the ability of a material to resist attack and degradation by various air- and soil-borne micro-organisms.

Migration – the absorption of oil or vehicle from a compound into an adjacent porous surface.

Mil – a unit of measure, one mil is equal to 0.001 inches, or 25.4 micrometers (um), often used to indicate the thickness of a roofing membrane.

Mildew – a superficial growth produced on organic matter or living plants by fungi.

Millimeter – a unit of measure equal to one thousandth (0.001) of a meter, or 0.03937 inches.

MIMA – Mineral Insulation Manufacturers Association

Mineral fiber – insulation composed principally of fibers manufactured from rock, slag or glass, with or without binders.

Mineral Granules – Natural or synthetic aggregate, ranging in size from 500?m (1?m 10-6m) to 1/4 in. diameter, used to surface BUR or modified bitumen cap sheets, asphalt shingles, and some cold process membranes.

Mineral stabilizer – a fine, water-insoluble inorganic material, used in a mixture with solid or semi-solid bituminous materials.

Mineral-surfaced roofing – roofing materials whose surface or top layer consists of granule-surfaced sheet.

Mineral-surfaced sheet – a roofing sheet that is coated on one or both sides with asphalt and surfaced with mineral granules.

Miter – the joint produced by joining two diagonally cut pieces.

Miter joint – a joint between two members at an angle to each other; each member is cut at an angle equal to half the angle of the junction; usually the members are at right angles to each other.

Model (building) codes – a compilation of standards or codes established to provide uniformly in regulations pertaining to building construction.

Model Codes – Codes established to provide uniformity in regulations pertaining to building construction. Examples: Uniform Building Code published by lCBO National Building Code by BOCA Standard Building Code by SBCCI International Building Code (New)

Modified bitumen – (1) a bitumen modified by including one or more polymers (e.g., atactic polypropylene, styrene butadiene styrene, etc.); (2) composite sheets consisting of a polymer modified bitumen often reinforced with various types of mats or films and sometimes surfaced with films, foils or mineral granules.

Moisture conduction – Migration by wicking as contrasted to vapor movement.

Moisture contour map—A map with lines connecting continuous levels of moisture. When drawn by computer the wettest areas are often indicated by darkest symbols and the driest areas left blank.

Moisture contour map – a map used to graphically define the location of moisture within a roof assembly after a moisture scan has been performed.

Moisture relief vent – a venting device installed through the roofing membrane to relieve moisture vapor pressure from within the roofing system.

Moisture scan – the use of a mechanical device (capacitance, infrared, or nuclear) to detect the presence of moisture within a roof assembly. (see Non-destructive testing.)

Mole run – A meandering ridge in a membrane not associated with insulation or deck joints.

Monolithic – formed from or composed of a single material; seamless.

Monomer – A simple molecule, which is capable of combining with a number of like or unlike molecules to form a polymer.

Mop-and-flop – A application procedure in which roof components (insulation boards, felt plies, cap sheets, etc.), are initially placed upside down adjacent to their ultimate locations, are coated with adhesive, and are then turned over and adhered to the substrate.

Mopping – Application of hot bitumen with a mop or mechanical applicator to the substrate or to the plies of a built-up or modified-bitumen roof. There are four types of mopping: (1) solid—a continuous coating; (2) spot—bitumen is applied in roughly circular areas, generally about 460 mm (18 in.) in diameter, leaving a grid of unmopped, perpendicular area, (3) strip— bitumen is applied in parallel bands, generally 200 mm (8 in.) wide and 300 mm (12 in) apart; (4) sprinkle—bitumen is shaken on the substrate from a broom or mop in a random pattern.

Mud cracking – surface cracking resembling a dried mud flat.

Mud slab – a layer of concrete, typically 2 inches (50 mm) to 6 inches (150 mm) thick, used as the substrate for membrane waterproofing.

Multiple Coat – two or more layers of coating applied to a substrate.

NAHB – National Association of Home Builders

Nail-type concrete anchor – A hammer-driven fastener with spiral or annular rings that provides pullout strength.

Nailer – (sometimes referred to as blocking) a piece or pieces of dimensional lumber and/or plywood secured to the structural deck or walls, which provide a receiving medium for the fasteners used to attach membrane or flashing.

Nailing – the application of nails. May be (1) exposed nailing of roofing wherein nail heads are exposed to the weather; (2) concealed nailing of roofing wherein nail heads are concealed from the weather by an overlapping material.

NBP – acrylonitrile butadiene polymer blend. One proprietary NBP membrane is commonly referred to as nitrile butadiene copolymer.

Needle Punched Fabric – a fabric where barbed needles (in multiple punches) achieve mechanical bonding/locking or carding of fibers.

Negative side waterproofing – an application wherein the waterproofing system and source of hydrostatic pressure are on opposite sides of the structural element.

Neoprene – Synthetic rubber (polychloroprene) used in liquid or sheet-applied elastomeric roofing membranes or flashing.

Nesting – (1) the installation of new metal roof deck directly on top of existing metal roof deck; (2) a method of reroofing with new asphalt shingles over existing shingles in which the top edge of the new shingle is butted against the bottom edge of the existing shingle.

Net free vent area – the area (measured in square inches) open to unrestricted air flow and commonly used as a yardstick to measure relative vent performance; the area of the opening of a vent minus the area displaced by the screening material.

Newton (N) – SI unit of measure for force.

NICA – National Insulation Contractors Association

Night seal (or night tie-in) – a material and/or method used to temporarily seal a membrane edge during construction to protect the roofing assembly in place from water penetration. Usually removed when roofing application is resumed.

Ninety-Pound – a prepared organic felt roll roofing with a granule surfacing that has a mass of approximately 90 pounds per 100 square feet, (4400 g/m²).

NIST – National Institute of Standards and Technology

Nitrile alloy – an elastomeric material of synthetic non-vulcanizing polymers.

Nitrile rubber – A family of copolymers of butadiene and acrylonitrile that can be vulcanized into tough oil resistant compounds. Blends with PVC are used where ozone and weathering are important requirements in addition to its inherent oil and fuel resistance.

No-cutout shingles – shingles consisting of a single solid strip with no cutouts.

Noble – in reference to metal, inert; opposite of active.

Noble metal – a metal that readily receives electrons from an anodic metal (see Galvanic series).

Non-Breathing Membrane – a membrane that does not allow significant amounts of water vapor or air to pass through; which has a perm rating 1.0 or less per ASTM E 96, Procedure E.

Non-traffic bearing – for waterproofing purposes, a membrane system requiring some form of protection barrier and wearing surface.

Non-Vulcanized Membrane – a membrane manufactured from thermoplastic compounds that retains its thermoplastic properties throughout the service life of the membrane.

Non-destructive testing (NDT) – a method to evaluate the disposition, strength or composition of materials or systems without damaging the object under test. Typically used to evaluate moisture content in roofing assemblies, the three common test methods are electrical capacitance, infrared thermography and nuclear back-scatter.

Nonflammable – not easily ignited and not burning rapidly if ignited.

Non-friable – a material that, when dry, cannot be crumbled, pulverized or reduced to powder by hand pressure.

Nonoxidizing – a material which resists oxidation in exterior exposures or accelerated weathering.

Nonvolatile content – the portion of a coating that does not evaporate during drying or curing under specified conditions, comprising the binder and, if present, the pigment. (The percent volatile content is obtained by subtracting the nonvolatile content from 100.).

Nonwoven – a term used to describe the random arrangement of reinforcing fibers (glass, polyester, etc.) in a mat or scrim.

Nonwoven fabric – a textile structure produced by bonding or interlocking of fibers, or both, accomplished by mechanical, chemical, thermal, or solvent means and combinations thereof.

Nuclear hydrogen detection (NHD) meter – a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflecting neutrons are measured by a gauge that is used to detect hydrogen; the quantity of hydrogen detected may be linked to the pressure of water.

Nuclear Testing (Nuclear Back-Scatter) – a device that contains a radioactive source to emit high velocity neutrons into a roof system. Reflecting neutrons are measured by a gauge that is used to detect moisture.

Nylon – generic name for a family of polyamide polymers, used as a scrim in some fabric-reinforced sheeting.

Off-ratio foam – SPF which has excess isocyanate or resin. Off-ratio will not exhibit the full physical properties of normal SPF.

Olefin – An unsaturated open-chain hydrocarbon containing at least one double bond: ethylene or propylene.

Olefin plastics – Plastics based on polymers made by the polymerization of olefins or copolymerization of olefins with other monomers, the olefins being at least 50 mass %.

Open valley – a method of valley construction in which the steep-slope roofing on both sides are trimmed along each side of the valley, exposing the valley flashing.

Open time – the period of time after an adhesive has been applied and allowed to dry, during which an effective bond can be achieved by joining the two surfaces.

Organic, adj. – Composed of hydrocarbons or their derivatives, or matter of plant or animal origin.

Organic coating – Coatings that are generally inert or inhibited. May be temporary (e.g., slushing oils) or permanent (paints, varnishes, enamels, etc.).

Organic felt – an asphalt roofing base material manufactured from cellulose fibers.

Organic shingle – an asphalt shingle reinforced with material manufactured from cellulose fibers.

Osmosis – movement of a solvent through a semipermeable membrane into a solution of higher solute concentration that tends to equalize the concentration of solute on the two sides of the membranes.

Overflow drainage – component in a roof drainage system used to protect the roof against damage from a water load imposed by blocked or partially blocked primary drainage system; e.g., overflow scupper, overflow interior drain.

Overspray surface texture – in SPF roofing, a condition of the foam in which the surface shows a linear coarse textured pattern and/or a pebbled surface. This surface is generally downwind of the sprayed polyurethane path and, if severe, unacceptable for proper coating coverage and protection.

Overspray – undesirable depositions of airborne spray.

Pallet – a platform (typically wooden) used for storing and shipping materials.

Pan – the bottom flat part of a roofing panel which is between the ribs of the panel.

Pan former – power roll-forming equipment that produces a metal roofing panel from a flat sheet.

Parapet wall – the part of a perimeter wall that extends above the roof.

Parge – in masonry construction, a coat of cement mortar on the face of rough masonry, the earth side of foundation and basement walls, or the like.

Partially attached – a roofing assembly in which the membrane has been “spot affixed” to a substrate, usually with an adhesive or a mechanical device.

Parting agent – a material applied to one or both surfaces of a sheet to prevent blocking.

Pascal (N/m²) – SI unit of measure for force per unit area.

Pass – 1) a layer of material, usually applied by the spray method, that is allowed to reach cure before another layer (“pass”) is applied; 2) a term used to explain a spray motion of the foam gun in the application of the spray polyurethane foam (SPF) material. The speed of the pass controls the thickness of the SPF.

Pass line – the junction of two passes of SPF. A distinct line is formed by the top skin of the bottom pass and the next pass adhering to this skin.

Pea gravel – Small gravel with a diameter approaching that of a pea. Size roughly defined by ASTM D448, Number 7 or smaller.

Peak – The uppermost point of a gable.

Pedestal – a support or base for roof top components such as pavers, pipes and small roof top units.

Peel strength – the average load per unit width required to separate progressively a flexible member from a rigid member or another flexible member.

Penetration-(1) any construction (e.g., pipes, conduits, HVAC supports) passing through the roof; (2) the consistency of a bituminous material expressed as the distance, in tenths of a millimeter (0.1 mm), that a standard needle penetrates vertically into a sample of material under specified conditions of loading, time, and temperature.

Percent Elongation – in tensile testing, the increase in the gauge length of a specimen measured at or after fracture of the specimen within the gauge length. Usually expressed as a percentage of the original gauge length.

Perlite – An aggregate used in lightweight insulating concrete and in preformed perlite insulating board, formed by heating and expanding siliceous volcanic glass.

Perm—(vapor transmission) Unit to measure water vapor transmission—one grain of water vapor per square foot per hour per inch of mercury pressure difference. 1 Perm = 1 grain/h•ft2•in. Hg = 5.74 x 10-11 kg/Pa•s•m2.

Permeability – (1) the capacity of a porous material to conduct or transmit fluids; (2) the time rate of vapor transmission through unit area of flat material of unit thickness induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. The English (inch.pound) unit of measurement for permeability is gr/hr.ft2.(in. Hg/in.), which is commonly referred to as “perm.inch” units.

Permeance – (1) the rate of water vapor transmission per unit area at a steady state through a material, membrane, or assembly; (2) the time rate of water vapor transmission through unit area of flat material or construction induced by unit vapor pressure difference between two specific surfaces, under specified temperature and humidity conditions. The English (inch.pound) unit of measurement for permeance is gr/h.ft2.in. Hg, which is commonly referred to as “perm” units.

Petroleum pitch – A dark brown to black, predominantly aromatic, solid cementitious material obtained by the processing of petroleum, petroleum fractions, or petroleum residuals.

pH – a measure of the acidity or alkalinity of a solution, with neutrality represented by a value of 7, with increasing acidity represented by increasingly smaller values, and with increasing alkalinity represented by increasingly larger values.

Phased application – the installation of a roofing or waterproofing system during two or more separate time intervals or different days. Application of surfacings at different time intervals are typically not considered phased application. (see Surfacing.) A roofing system not installed in a continuous operation.

Phenolic plastics – Plastics based on resins made by the condensation of phenols, such as phenol and cresol, with aldehydes.

Picture framing – A rectangular pattern of ridges in a membrane over insulation or deck joints.

Pigment – an insoluble compounding material used to impart color.

Pig spout – A sheet metal flashing designed to direct the flow of water out through the face of the gutter rather than through a downspout.

PIMA – Polyisocyanurate Insulation Manufacturers Association

Pinhole – A tiny hole in a coating, film, foil, or laminate comparable in size to one made by a pin.

Pipe boot – prefabricated flashing piece used to flash around circular pipe penetrations.

Pitch – See Incline; Coal Tar Pitch; or Petroleum Pitch.

Pitch-pocket (Pitch-pan) – a flanged, open bottomed enclosure made of sheet metal or other material, placed around a penetration through the roof, filled with grout and bituminous or polymeric sealants to sealants to seal the area around the penetration.

Pittsburgh lock seam – a method of interlocking metal, usually at a slope change.

Plastic – A material that contains as an essential ingredient one or more organic polymeric substances of large molecular weight. It is solid in its finished state and at some stage in its manufacture or processing into finished articles can be shaped by flow.

Plastic cement – a roofing industry generic term used to describe asphalt roof cement that is a trowelable mixture of solvent-based bitumen, mineral stabilizers, and other fibers and/or fillers. Generally, intended for use on relatively low slopes, not vertical surfaces. (also see Asphalt roof cement and Flashing cement.)

Plastic Film – a flexible sheet made by the extrusion of thermoplastic resins.

Plasticizer – Material, frequently solvent-like, incorporated in a plastic or a rubber to increase its ease of workability, flexibility, or extensibility. Adding the plasticizer may lower the melt viscosity, the temperature of the second order transition, or the elastic modulus of the polymer.

Plasticizer migration – in some thermoplastic roofing membranes, the loss of plasticizer chemicals from the membrane, resulting in shrinkage and embrittlement of the membrane, typically PVC.

Plasticizers – May be monomeric liquids (phthalate esters), low molecular weight liquid polymers (polyesters) or rubbery high polymers (EVA). The most important use of plasticizers is with PVC where the choice of plasticizer dictates under what conditions the membrane may be used.

Plastomeric – a plastic-like polymer consisting of any of various complex organic compounds produced by polymerization, and capable of being molded, extruded, or cast into various shapes or films.

Pliability – the material property of being flexible or moldable.

Ply – A layer of felt in a roofing membrane; a four-ply membrane should have at least four plies of felt at any vertical cross section cut through the membrane.

Ply (Plywood)—A single veneer lamina in a glued plywood panel.

Plywood – A flat panel built up of sheets of wood veneer called plies, united under pressure by a bonding agent to create a panel with an adhesive bond between plies as strong as or stronger than, the wood. Plywood is constructed of an odd number of layers with grain of adjacent layers perpendicular. Layers may consist of a single ply or two or more plies laminated with parallel grain direction. Outer layers and all odd numbered layers generally have the grain direction oriented parallel to the long dimension of the panel.

PMR – protected membrane roof.

Pointing—(1) Troweling mortar into a joint after masonry units are laid. (2) Final treatment of joints in cut stonework. Mortar or putty-like filler is forced into the joint after the stone is set.

Polychloroprene – see Neoprene.

Polyester – a polymer in which the repeated structural unit in the chain is of the ester type.

Polyester fiber – Generic name for a manufactured fiber in which the fiber-forming substance is any long chain synthetic polymer composed of an ester of a dihydric alcohol and terephthalic acid. Scrims made of polyester fiber are used for fabric reinforcement.

Polyisobutylene – The polymerization product of isobutylene varying in consistency from a viscous liquid to a rubberlike solid, with corresponding variation in molecular weight from 1,000 to 400,000. May be compounded for use as a roof membrane material.

Polyisocyanurate – Thermoset polymer formed by polymerization of isocyanate; rigid foam insulation meeting ASTM C1289; a thermal insulation similar in appearance to polyurethane foam, but with improved fine resistance or rating.

Polymer – A macromolecular material formed by the chemical combination of monomers having either the same or different chemical composition. Plastics, rubbers, and textile fibers are all high molecular weight polymers.

Polymer modified bitumen – see Modified bitumen.

Polymeric methylene diphenyl diisocyanate (PMDI) – component A in SPF. An organic chemical compound having two reactive isocyanate groups. It is mixed with the B component to form polyurethane.

Polymerization – a chemical reaction in which monomers are linked together to form polymers.

Polyol – a polyhydric alcohol, i.e., one containing three or more hydroxyl groups, one component of polyisocyanurate and polyurethane compounds.

Polypropylene – a polymer prepared by the polymerization of propylene as the sole monomers.

Polystyrene – a polymer prepared by the polymerization of styrene as the sole monomer.

Polyvinyl Chloride (PVC) – A synthetic thermoplastic polymer prepared from vinylchloride. PVC can be compounded into flexible and rigid forms through the use of plasticizers, stabilizers, filler, and other modifiers; rigid forms used in pipes; flexible forms used in manufacture of sheeting and roof membrane materials.

Pond – A roof area that retains water instead of draining after rainfall.

Ponding – the excessive accumulation of water at low-lying areas on a roof that remains after the 48 hours after the end rainfall under conditions conducive to drying.

Pop rivet – a relatively small-headed pin with an expandable head for joining light gauge sheet metal.

Popcorn surface texture – in SPF roofing, the condition in which the foam surface shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

Positive drainage – the drainage condition in which consideration has been made during design for all loading deflections of the deck and additional roof slope has been provided to ensure drainage of the roof area within 48 hours of rainfall during conditions conducive to drying.

Positive side waterproofing – an application where the waterproofing systems and the source of the hydrostatic pressure are on the same side of the structural element.

Pot life (Working life) – the period of time during which a reacting composition remains suitable for its intended processing after mixing with reaction initiating agents.

Pourable sealer – a type of sealant often supplied in two parts and used at difficult-to-flash penetrations, typically in conjunction with pitch-pockets to form a seal.

Pre-tinning – coating a metal with solder or tin alloy prior to soldering or brazing it.

Pre-painted coil – Coil steel which receives a paint coating prior to the forming operation.

Pre-tinning – coating a metal with solder or tin alloy prior to soldering or brazing it.

Press brake – A machine used in cold-forming metal sheet or strip into desired profiles.

Prestressed concrete – Concrete in which the reinforcing cables, wires, or rods in the concrete are tensioned before there is load on the member, holding the concrete in compression for greater strength.

Preventive maintenance – The regular, scheduled, inspection for and the repair of normal, expected breakdown of materials and equipment.

Prime coat – First liquid coat applied in a multiple coat system.

Primer-(1) a thin, liquid-applied solvent-based bitumen that may be applied to a surface to improve the adhesion of subsequent applications of bitumen; (2) a material which is sometimes used in the process of seaming single-ply membranes to prepare the surfaces and increase the strength (in shear and peel) of the field splice; (3) a thin liquid-applied material that may be applied to the surface of SPVF to improve the adhesion of subsequent application of SPVF protective coatings.

Proportioner – the basic pumping unit for SPF or two-component coating systems. Consists of two positive displacement pumps designed to dispense two components at a precisely controlled ratio.

Protected membrane roof (PMR) – an insulated and ballasted roofing assembly in which the insulation and ballast are applied on top of the membrane (sometimes referred to as an “inverted roof assembly”).

Protection course – a sacrificial material used to shield a waterproofing material from damaging external forces.

Psychrometer – an instrument used to measure humidity in the atmosphere from two thermometers which are similar except that the bulb of one is kept wet, the bulb of the other being dry.

Psychrometric chart – chart showing the relationship between dew point temperature, dry bulb temperature, wet bulb temperature and relative humidity.

Puncture resistance – the ability of a material to withstand the action of a penetrating or puncturing object.

Purlin – horizontal secondary structural member that transfers loads from the primary structural framing.

PVC – polyvinyl chloride.

R-Factor – Resistance to heat flow. The summation of individual thermal resistances in an assembly.

R-value – see Thermal resistance.

Racking – a method of asphalt shingle application, also referred to as the straight-up method, whereby shingle courses are applied vertically, up the roof rather than laterally or across and up.

Rafter

one of a series of sloped structural members, that extend from the ridge or hip to the downslope perimeter or eave, designed to support the roof deck and its associated loads.

Raggle – a groove or slot, often cut in a masonry wall or other vertical surface adjoining a roof, for inserting an inset flashing component such as a reglet.

Rake – The sloped edge of a roof at the first or last rafter.

Rake angle – Angle fastened to purlins at rake for attachment of endwall panels.

Rake-starter (Bleeder strip) – starter-strip used along rake edges in conjunction with asphalt shingle roofing.

Re-cover – the addition of a new roof membrane or steep-slope roof covering over a major portion of an existing roof assembly. This process does not involve removal of the existing roofing.

Reflectivity – see Light reflectance.

Reglet – a sheet metal receiver for the attachment of counterflashing. A reglet may be surface-mounted, inset into a raggle or embedded behind cladding.

Reinforced membrane – a roofing or waterproofing membrane that has been strengthened by the addition or incorporation of one or more reinforcing materials, including woven or nonwoven glass fibers, polyester mats or scrims, nylon, or polyethylene sheeting.

Relative humidity – The ratio of the mass per unit volume (or partial pressure) of water vapor in an air-vapor mixture to the saturated mass per unit volume (or partial pressure) of the water vapor at the same temperature, expressed as a percentage.

Release tape (or strip) – a plastic film or paper strip that is applied to the back of self-sealing shingles and other materials. The strip prevents the material from sticking together in the roll or bundle. With asphalt shingles, the strip need not be removed for application of the shingles.

Replacement – the practice of removing an existing roof system down to the roof deck and replacing it with a new roofing system.

Remedial roofing – The repair of selected isolated portions of the roof system to return the roof to uniform condition. This normally involves the removal of wet materials along with correction of the original cause of the problem.

Reroofing – the process of re-covering, or tearing-off and replacing an existing roof system.

Resin – component B in SPF. This component contains a catalyst, blowing agent, fire retardants, surfactants and polyol. It is mixed with the A component to form polyurethane.

Resistance, Thermal – the average temperature difference between two defined surfaces of a particular body or assembly when unit thermal transmission in unit time through unit area is established between the surfaces. R=_Fòhòsòft2/Btu (R=Kòm2/W).

Retrofit – the modification of an existing building or facility to include new systems or components.

Ridge – Highest point on the roof of the building, a horizontal line running the length of the building.

Ridge cap – A material or covering applied over the ridge of a roof.

Ridge course – the last or top course of roofing materials, such as tile, roll roofing, shingles, etc., that covers the ridge and overlaps the intersecting field roofing.

Ridge vent – a ventilator located at the ridge that allows the escape of warm and/or moist air from the attic area or rafter cavity.

Ridging – An upward, tenting displacement of a membrane, frequently over an insulation joint.

RIEI – Roofing Industry Educational Institute

RMA – Rubber Manufacturers Association

Roll goods – A general term applied to rubber and plastic sheeting, usually furnished in rolls.

RMA – Rubber Manufacturers Association

Roll roofing – Coated felts, either smooth or mineral surfaced.

Roof – (1) the cover of a building; (2) to cover with a roof.

Roof area divider – refer to area divider.

Roof area expansion joint – see expansion joint.

Roof assembly – an assembly of interacting roof components including the roof deck, vapor retarder (if present), insulation, and roof covering.

Roof cement – see Asphalt roof cement or Coal tar roof cement.

see Flashing Cement.

Roof covering – the exterior roof cover or skin of the roof assembly, consisting of membrane, panels, sheets, shingles, tiles, etc.

Roof curb – raised frame used to mount mechanical units (such as air conditioning or exhaust fans), skylights, etc. on a roof.

Roof Diaphragm – a structural roof deck that is capable of resisting shear that is produced by lateral forces, such as wind or seismic loads.

Roofer – craftsman who applies roofing materials.

Roof jack – An accessory used to cover pipes (such as vents or flues) that penetrate the roof panel.a metal or wood bracket used to support toe-boards on steep-slope roofs. (also see Flashing Collar.)

Roof or Roofer’s Cement – see Asphalt Roof Cement or Coal Tar Roof Cement.

Roof overhang – A roof extension beyond the endwall/sidewall of a building.

Roof seamer – Machine that crimps panels together or that welds laps of E/P systems using heat, solvent or dielectric energy.

Roof slope – the angle a roof surface makes with the horizontal, expressed as a ratio of the units of vertical rise to the units of horizontal length (sometimes referred to as run). For English units of measurement, when dimensions are given in inches, slope may be expressed as a ratio of rise to run, such as 4:12 or as an angle.

Roofing system – a system of interacting roof components, generally consisting of membrane or primary roof covering and roof insulation (not including the roof deck) designed to weatherproof and, sometimes, to improve the building’s thermal resistance.

Rosin paper (specifically Rosin-sized sheathing paper) – a nonasphaltic paper used as a sheathing paper or slip sheet in some roof systems.

Rubber – A material capable of quickly recovering from large deformations, normally insoluble in boiling solvent such as benzene, methyl ethyl ketone, and ethanol toluene azeotrope. A rubber in its modified state retracts within 1 mm to less than 1.5 times its original length after being stretched to twice its length.

Run – horizontal dimension of a slope.

Rust Blush – the earliest stage of rusting characterized by the orange or red color. Occurs frequently on freshly sand blasted steel if allowed to stand too long before coating.

Saddle – A small structure that helps to channel surface water to drains. Frequently located in a valley, a saddle is often constructed like a small hip roof or like a pyramid with a diamond-shaped base (also see Cricket).

Sag – undesirable excessive flow in material after application to a surface.

Sandwich panel – A panel assembly used as covering; consists of an insulating core material with inner and outer skins.

Saturated felt – a felt that has been immersed in hot bitumen; the felt adsorbs as much bitumen as it can retain under the processing conditions, but remains porous and contains voids.

SBA – Systems Builders Association

SBS – see Styrene butadiene styrene.

Scarf – To scrap or abrade a surface to remove degraded or wet polyurethane foam.

Scarfed – shaped by grinding.

Screeding – the process of striking off excess concrete to bring the top surface of the concrete to the proper finish and elevation.

Screen wall – a nonstructural wall erected around units or curbs on a roof. Typically the framing consists of girts with a wood or metal covering attached to the frame.

Scrim – a woven, nonwoven or knitted fabric composed of continuous strands of material used for reinforcing or strengthening membranes.

Scupper – Channel through parapet, designed for peripheral drainage of the roof, usually a safety overflow to limit accumulation of ponded rainwater caused by clogged drains. Drainage device in the form of an outlet through a wall, parapet wall or raised roof edge lined with a soldered sheet metal sleeve.

Scuttle – a hatch that provides access to the roof from the interior of the building.

SDI – Steel Deck Institute.

Seal – (1) a generic term for a function that prevents or controls the passage of water; (2) to secure a roof or structure from the entry of moisture.

Sealant-(1) a material that has the adhesive and cohesive properties to form a seal; (2) a mixture of polymers, fillers, and pigments used to fill and seal joints where moderate movements is expected; unlike caulking, it cures to a resilient solid.

Sealant backing – a compressible material placed in a joint before applying a sealant.

Sealer – a coating designed to prevent excessive absorption of finish coats into porous surfaces; a coating designed to prevent bleeding.

Sealing washer – a rubber or neoprene washer, sometimes metal-backed, typically placed on a fastener to prevent water from migrating into a through the fastener hole.

Seam – a joint formed by mating two separate sections of material. Seams can be made or sealed in a variety of ways, including adhesive bonding, hot-air welding, solvent welding, using adhesive tape, sealant, etc.

Seam sample – in single-ply and sometimes modified bitumen membrane roofing, a sample from the membrane that extends through the side lap of adjacent rolls of membrane, taken for the purpose of assessing the quality of the seam.

Seam strength – Strength of a seam of material measured either in shear or peel modes, reported either in absolute units, e.g., pounds per inch of width–or as a percent of the sheeting strength.

Self-adhering membrane – a membrane that can adhere to a substrate and to itself at overlaps without the use of an additional adhesive. The undersurface of a self-adhering membrane is protected by a release paper or film, which prevents the membrane from bonding to itself during shipping and handling.

Self-drilling screw – A fastener that drills and taps its own hole, used as a fastener for attaching panels to purlins and girts.

Self-sealing shingle – an asphalt shingle containing factory-applied strip or spots of heat sensitive adhesive intended to adhere the overlying shingle once installed on the roof and warmed by the sun.

Self-tapping screw – A fastener that forms receiving threads when turned into a previously drilled hole. It is for attaching panels to purlins and girts and for

connecting trim and flashing.

Self-Vulcanized Membrane – a membrane manufactured from compounds that are thermoplastic during manufacture and installation, but whose polymers eventually cross-link and cure during exposure.

Selvage – (1) an edge or edging that differs from the main part of a fabric, granule-surfaced roll roofing or cap sheet, or other material; (2) a specially defined edge of the material (lined for demarcation), which is designed for some special purpose, such as overlapping or seaming.

Selvage Edge – an edge designed for certain sheet good materials, e.g., mineral-surfaced sheets. With mineral surfaced sheets, the surfacing is omitted over a portion of the longitudinal edge of the sheet (e.g., mineral surface cap sheet) in order to obtain better adhesion of the overlapping sheet.

Separator layer – refer to Slip sheet.

Service life – Anticipated useful life of a building, building component or building subsystem (e.g., roof system).

Service temperature limits – the minimum or maximum temperature at which a coating, SPF, or other material will perform satisfactorily.

Set – to convert into a fixed or hardened state by chemical or physical action.

Shading – slight differences in surfacing color, such as shingle granule coloring, that may occur as a result of manufacturing operations.

Shark fin – Curled felt projecting upward through the flood coat and aggregate of a BUR membrane.

Shear – The force tending to make two contacting parts slide upon each other in opposite directions parallel to their plane of contact.

Shear strength – the resistance to forces that cause or tend to cause two contiguous parts of the body to slide relative to each other in a direction parallel to their contrast.

Shed roof – a roof having only one sloping plane and no hips, ridges or valleys.

Sheeting – A form of plastic or rubber in which the thickness is very small in proportion to length and width and in which the polymer compound is present as a continuous phase throughout, with or without fabric.

Shelf life – the maximum time a package material can be stored under specified conditions and still meet the performance requirements specified.

Shingle—(1) A small unit of prepared roofing designed for installation with similar units on overlapping rows on inclines normally exceeding 25%; (2) T o cover with shingles, and (3) T o apply any sheet material in overlapping rows like shingles.

Shingling—(1) The procedure of laying parallel felts so that one longitudinal edge of each felt overlaps, and the other longitudinal edge underlaps an adjacent felt. (See also Ply). Normally, felts are shingled on a slope so that the water flows over rather than against each lap; (2) The application of shingles to a sloped roof.

Shore “A” Hardness – a measure of firmness of a material by means of a Durometer Hardness Gauge. (A measure of 20 is about the firmness of a gum eraser; 90 is about that of a rubber heel.)

Shrinkage – a decrease in one or more dimensions of an object or material.

Shrinkage crack – in waterproofing, a separation in a material, such as a concrete substrate, caused by the inability of the material to resist a reduction in size which occurs during its hardening or curing process or both.

SI – an abbreviation for the International System of Units (Le Systeme International d’Unites).

Side lap – the continuous longitudinal overlap of neighboring like materials.

Side lap fastener – a fastener used to connect adjacent panels together at the side lap.

Siding – the finish covering of an exterior wall of a frame building; the siding may be cladding material such as wood, aluminum or vinyl (but not masonry).

Sieve – An apparatus with square apertures for separating sizes of material.

Silicone-based Water Repellants – any of the organopolysiloxanes (silicone derivative) applied to masonry materials for dampproofing or repelling water.

Sill – The bottom horizontal framing member of an opening such as a window or door.

Sill flashing – a flashing of the bottom horizontal framing member of an opening, such as below a window or door.

Single Coverage – roofing material that provides one layer over the substrate to which it is applied.

Single-lock standing seam – a standing seam that uses one overlapping interlock between two seam panels, in contrast with the double interlocking used in a double standing seam.

Single-ply membranes – roofing membranes that are field applied using just one layer of membrane material (either homogeneous or composite) rather than multiple layers.

Single-ply roofing – a roofing system in which the principal roof covering is a single layer flexible membrane often of thermoset or thermoplastic membrane.

Single-Ply System – generally, there are six types of single-ply roofing systems 1) Fully-adhered 2) Loose-laid 3) Mechanically-fastened 4) Partially-adhered 5) Protected membrane roof 6) Self-adhering

Single slope – A sloping roof with one surface. The slope is from one wall to the opposite wall of rectangular building.

Siphon break – A small groove to arrest the capillary action of two adjacent surfaces.

Skinning – the formation of a dense film on the surface of a liquid coating or mastic.

Skirt flashing – a formed metal counterflashing secured under a mechanical unit or skylight to cover and protect the upper edge of a base flashing and its associated fasteners.

Skylight – an opening in a roof that is glazed with a transparent or translucent material; used to admit diffused light to the space below.

Slab – A semi-finished steel product, intermediate between ingot and plate, with the width at least twice the thickness.

Slab-on-grade – a horizontal placement of concrete placed directly over a prepared earth substrate.

Slag – a hard aggregate that is left as a residue from blast furnaces, which may be used as a surfacing material on certain (typically bituminous) roof membrane systems.

Slate – a hard, brittle metamorphic rock consisting mainly of clay minerals, used extensively as dimensional stone for steep roofing and in granular form as surfacing on some other roofing materials.

Slating hook – a steep-slope roofing attachment device, shaped like a hook, that can be used for fastening roofing slate.

Slip sheet – sheet material, such as reinforced kraft paper, rosin-sized paper, polyester scrim or polyethylene sheeting, placed between two components of a roof assembly (such as between membrane and insulation or deck) to ensure that no adhesion occurs between them and to prevent possible damage from chemical incompatibility, wearing or abrasion of the membrane.

Slit sample – in SPF roofing, a small cut about 1 inch x 1/2 inch (25 mm x 13 mm x 13 mm), in a half-moon shape, used to measure coating film thickness.

Slippage – Relative lateral movement of adjacent felts (or sheets) in a roof membrane. It occurs mainly in roofing membranes on a slope, sometimes exposing the lower plies or even the base sheet to the weather.

Slope – Tangent of the angle between the roof surface and the horizontal plane, expressed as a percentage, or in inches of rise per foot of horizontal distance. (See also Incline and Roof Slope).

SMACNA – Sheet Metal and Air Conditioning Contractors National Association.

Smooth surfaced roof – A roof membrane without mineral aggregate surfacing.

Smooth surface texture – in SPF roofing, the condition of the foam in which the surface shows spray undulation and is ideal for receiving a protective coating.

Snap-on cap – a separate cap that snaps on over the vertical legs of some single standing or batten seam metal roof systems.

Snow guard – a series of devices attached to the roof in a pattern that attempts to hold snow in place, thus preventing sudden snow or ice slides from the roof; any device intended to prevent snow from sliding off a roof.

Snow load – the live load due to the weight of snow on a roof; included in design calculations.

Soffit – The exposed underside covering of any exterior overhanging section of a roof eave, gable or sidewall.

Soffit vent – a premanufactured or custom built air inlet source located at the downslope eave or in the soffit of a roof assembly.

Softening point – the temperature at which bitumen becomes soft enough to flow, as determined by an arbitrary, closely defined method (ASTM Standard test method D 36 or D 3461).

Softening point drift – a change in the softening point of bitumen during storage or application. (see Fallback.)

Soil stack – a sanitation pipe that penetrates the roof; used to vent plumbing fixtures.

Solder – a lead/tin mixture that is melted and used to bond two pieces of some metals together.

Solid mopping – A continuous mopping of a surface.See Mopping. Sprinkle mopping—See Mopping.

Solids content – the percentage by weight of the nonvolatile matter in an adhesive.

Solvent – any liquid used to dissolve another material.

Solvent cleaners – used to clean some single-ply roofing membranes prior to splicing, typically including heptane, hexane, white gasoline, and unleaded gasoline.

Solvent welding – a process where a liquid solvent is used to chemically weld or join together two or more layers of certain membrane materials (usually thermoplastic).

Spalling – breaking off of plate-like pieces from a concrete, rock or masonry surface.

Special steep asphalt – asphalt complying with ASTM D 312, Type IV. (See Asphalt.)

Specification – a precise statement of a set of requirements to be satisfied by a material, product, system, or service.

SPF – sprayed polyurethane foam.

SPFA – Sprayed Polyurethane Foam Alliance (a business unit of the American Plastics Council).

SPF compound – a term used to describe the raw materials (isocyanate and resin) used to make polyurethane foam.

SPI – The Society of the Plastics Industry

SPI/SPFD – The Society of the Plastics Industry/Sprayed Polyurethane Foam Division

Splash block – a small masonry or polymeric block laid on the ground or lower roof below the opening of a downspout used to help prevent soil erosion and aggregate scour in front of the downspout.

Splice – bonding or joining of overlapping materials. (see Seam.)

Splice plate – a metal plate placed underneath the joint between two pieces of metal.

Split – a membrane tear resulting from tensile stresses.

Split Sheet – see Nineteen-Inch Selvage.

Split slab – a term used to describe two separate concrete slabs. The first is placed as a slab on grade or suspended slab, and covered with waterproofing and a drainage system. The second slab, also referred to as a topping slab, is then placed over the underlying slab and waterproofing.

Splice-tape – cured or uncured synthetic rubber tape used for splicing membrane materials.

Spot Mopping – a mopping pattern in which hot bitumen is applied in roughly circular areas, leaving a grid of unmopped, perpendicular bands on the roof.

Sprayed polyurethane foam (SPF) – a foamed plastic material, formed by spraying two components, PMDI (A component) and a resin (B component) to form a rigid, fully adhered, water-resistant, and insulating membrane.

Spread coating – a manufacturing process in which membranes are formed using a liquid compound that is spread onto a supporting reinforcement base layer and then dried to its finished condition.

SPRI – Single Ply Roofing Institute

Sprinkle Mopping – a random mopping pattern in which heated bitumen beads are strewn onto the substrate with a brush or mop.

Spud – To remove the roofing aggregate and most of the bituminous top coating by scraping and chipping.

Spudder – Heavy steel implement with a dull, bevel-edged blade for removing embedded aggregate from a BUR membrane surface.

Spunbond – a type of nonwoven fabric formed from continuous fiber filaments that are laid down and bonded continuously, without an intermediate step.

Spunlaced – a nonwoven fabric made by mechanically bonding a dry-laid staple fabric by water jet, which entangles the individual fibers.

Square-tab shingles – shingles with tabs that are all the same size and exposure.

Square – a unit used in measuring roof area equivalent to 100 square feet (9.29 m2) of roof area.

Squeegee – (1) a blade of leather or rubber set on a handle and used for spreading, pushing or wiping liquid material on, across or off a surface; (2) to smooth, wipe or treat with a squeegee.

Stack vent – A vertical outlet designed to relieve pressure exerted by water vapor between a membrane and the vapor retarder or deck.

Stainless steel – An alloy of steel which contains a high percentage of chromium. Also may contain nickel or copper. Has excellent resistance to corrosion.

Standing seam – Watertight seam type featuring an upturned rib, which may also be structural. It is made by turning up the edges of two adjacent metal panels and then folding them over in one of a variety of ways.

Standing water test – Evaluations in which test panels are submerged in aqueous solutions and alternately dried in air.

Starter course – the first layer of roofing, applied along a line adjacent to the downslope perimeter of the roof area. With steep-slope watershedding roof coverings, the starter course is covered by the first course.

Starting platform – A movable platform used to support a seaming machine as it begins to roll- seal a metal seam.

Starter sheets – (1) felt, ply sheet or membrane strips that are made or cut to widths narrower than the standard width of the roll and used to start the shingling pattern at an edge of the roof; (2) particular width sheets designed for perimeters in some mechanically attached and fully adhered single-ply systems.

Starter strip – roll roofing or shingle strips applied along the downslope eave line before the first course of roofing and intended to fill spaces between cutouts and joints of the first course.

Static load – any load, as on a structure, that does not change in magnitude or position with time.

Steel – a malleable alloy of iron and carbon produced by melting and refining pig iron and/or scrap steel; graded according to the carbon content (in a range from 0.02 to 1.7%); other elements, such as manganese and silicon, may be included to provide special properties.

Steel joist (open web steel joist) – normally used as a horizontal supporting member between beams or other structural members, suitable for the support of some roof decks.

Steep asphalt – A relatively viscous roofing asphalt conforming to the requirements of Specification D312, Type Ill.

Steep-Slope Roofing – a category of roofing that includes water shedding types of roof coverings installed on slopes exceeding 3 12 or 25%.

Steep-slope roofs – a category of roofing that generally include water-shedding types of roof coverings installed on slopes exceeding 3:12 (14 degrees).

Steeple – a tower or spire, usually located on a church.

Step flashing – individual pieces of sheet metal material used to flash walls, around chimneys, dormers and such projections along the slope of a roof. Individual pieces are overlapped and stepped up the vertical surface.

Stick clip – in waterproofing, a non-penetrating fastener that is adhered to the waterproofing surface; typically used to retain insulation, drainage panels, prefabricated protection materials, etc., against the waterproofing to prevent sliding and displacement.

Stiffener rib – small intermediate bends in a metal pan used to strengthen the panel.

Storm anchor – see Wind Clip.

Strain – the dimensionless expression for the elongation of a material under stress. Strain is expressed as the ratio of elongation per unit length.

Strapping (felts) – a method of installing roofing rolls or sheet good materials parallel with the slope of the roof.

Straw nail – a long-shanked nail. Sometimes used for fastening over tile at hips and ridges.

Strawberry – See Blueberry.

Stress—(1) A measure of the load on a structural member in terms of force per unit area (Mpa) (kips per sq. in.); (2) The force acting across a unit area in solid material in resisting the separation, compacting or sliding that tends to be induced by external forces. Also the ratio of applied load to the initial cross sectional area, or the maximum stress in the outer fibers due to an applied flexural load.

Stress concentration – A condition in which stress is highly localized, usually induced by an abrupt change in the shape of a member or at a substrate joint (e.g., between insulation joints)

Stress-Crack – external or internal cracks within a material caused by long-term stress. Environmental factors, such as contact with corrosive material, usually accelerate stress-cracking.

Stress relaxation – The time-dependent change in the stress resulting from application of a constant total strain to a specimen at a constant temperature. The stress-relaxation at a given elapsed time is equal to the maximum stress resulting when the strain is applied minus the stress at the given time.

Striations – a parallel series of small grooves, channels, or impressions typically within a metal roof panel used to help reduce the potential for oil-canning.

Strike-through – A term used in the manufacture of fabric reinforced polymeric sheeting to indicate that two layers of polymer have made bonding contact through the reinforcing scrim.

Strip Mopping – a mopping pattern in which hot bitumen is applied in parallel bands.

Strip shingles – asphalt shingles that are manufactured in strips, approximately three times as long as they are wide.

Strippable films – (for metal) added protection of plastic films sometimes applied to coated or finished metals after the coil coating process. Applied after prime and top coats to resist damage to the finish prior to and during shipping, fabrication, and installation.

Stripping in – application of membrane stripping ply or plies.

Stripping—Strip flashing: (1) The technique of sealing a joint between metal and bituminous membrane with one or two plies of felt or fabric and hot- or cold-applied bitumen; (2) The technique of taping joints between insulation boards or deck panels.

Structural panel – a metal roof panel designed to be applied over open framing rather than a continuous or closely spaced roof deck.

Styrene butadiene rubber

high molecular weight polymers having rubber-like properties, formed by the random copolymerization of styrene and butadiene monomers.

Substantial Completion – The stage in the progress of the work when it is sufficiently complete for the owner to occupy or utilize the work for its intended use.

Substrate – Surface upon which a roof component is placed (structural deck or insulation).

Sump – an intentional depression around a roof drain or scupper that promotes drainage.

Sump pan – a metal pan used to create a depression around a drain or scupper to enhance drainage.

Superimposed loads – loads that are added to existing loads. For example, a large stack of insulation boards placed on top of a structural steel deck.

Super-steep asphalt – A high viscosity roofing asphalt conforming to the requirements of Specification D312, Type IV.

Supported sheeting – See Fabric Reinforcement.

• Surface Conductance – a unit of heat flow or heat exchange between a material and the air around it. Ventilation over a surface will decrease the thickness of the air film and reduce the thermal effect (increase the heat flow).

Surface cure – Curing or vulcanization which occurs in a thin layer on the surface of a manufactured polymeric sheet or other items.

Surface Dryness – surface dryness can be evaluated qualitatively by taping an 18 inch by 18 inch (0.46 m by 0.46 m) clear 4 mil polyethylene sheet to a concrete surface, and observing the moisture that may collect on the underside of the polyethylene sheet. Additional details of this procedure may be found in ASTM D 4263.

Surface erosion – the wearing away of a surface due to abrasion, dissolution or weathering.

Surface texture – the resulting surface from the final pass of SPF. The following terms are used to describe the different SPF surface textures: smooth orange peel, coarse orange peel, verge of popcorn, popcorn, treebark, and oversprayed.

Surfacing – the top layer or layers of a roof covering, specified or designed to protect the underlying roofing from direct exposure to the weather.

Surfactants – Surface active agents that reduce surface tension when dissolved in water or water solutions, or reduce interfacial tension between two liquids, or between a liquid and a solid.

Synthetic Rubber – any of several elastic substances resembling natural rubber, prepared by the polymerization of butadiene, isoprene, and other unsaturated hydrocarbons. Synthetic rubber is widely used in the fabrication of single-ply roofing membranes.

Susceptibility – When not otherwise qualified, the degree of change in viscosity with temperature.

SWRI – Sealant, Waterproofing and Restoration Institute

T-joint – the condition created by the overlapping intersection of three or four sheets in the membrane.

Tab – the exposed portion of strip shingles defined by cutouts.

Tack-free – A film is considered tack-free when the finger, with a slight pressure, will not leave a mark. The surface will not be sticky.

Tack-free time – in SPF-based roofing, a curing phase of polyurethane foam to when the material is no longer sticky. When the polyurethane foam is tack free, it can be sprayed over with another pass, referred to as a “lift”. With some care the polyurethane foam can be walked on soon after it is tack free.

Talc – whitish powder applied at the factory to the surface of some roofing materials (e.g., vulcanized EPDM membranes), used as a release agent to prevent adhesion of the membrane to itself.

Tapered edge strip – A tapered insulation strip used to elevate the roofing at the perimeter and at penetrations and at curbs, and to provide gradual transition from one layer of insulation to another.

Taping – (1) the technique of connecting joints between insulation boards or deck panels with tape; (2) the technique of using self-adhering tape-like materials to seam or splice single-ply membranes.

Tar – a brown or black bituminous material, liquid or semi-solid in consistency, in which the predominating constituents are bitumens obtained as condensates in the processing of coal, petroleum, oil-shale, wood, or other organic materials.

Tar boils – Bubbles of moisture vapor encased in a thin film of bitumen, also known as blueberry, blackberry, etc.

Tarred felt – see Coal tar felt.

Tear resistance – the load required to tear a material, when the stress is concentrated on a small area of the material by the introduction of a prescribed flaw or notch. Expressed in psi (pounds force) per inch width or kN/m (kilonewton per meter width).

Tear strength – The maximum force required to tear a specified specimen, the force acting substantially parallel to the major axis of the test specimen. Measured in both initiated and uninitiated modes. Obtained value is dependent on specimen geometry, rate of extension.

Tear-off – Removal of a failed roof system down to the structural deck surface.

Tear-off and reroof – the removal of all roof system components down to the structural deck, followed by installation of a completely new roof system.

Tensile Fatigue Resistance – the ability of a given membrane material to resist “fatigue” and/or other damage (such as loss of elasticity) caused by the alternate stretching and relaxing of the material over a period of time.

Tensile strength

the strength of a material under tension as distinct from torsion, compression or shear.

Tensile Test – a test in which a specimen is subjected to increasing longitudinal pulling stress until fracture occurs.

Tension leveling – the process of pulling metal coil stock between two spools under a certain pressure to help reduce side camber and potential oil canning in the coil stock caused by manufacturing and cutting processes.

Termination – the treatment or method of anchoring and/or sealing the free edges of the membrane in a roofing or waterproofing system.

Terne – an alloy of lead and tin, used to coat sheets of carbon steel or stainless steel for use as metal roofing sheet.

Terra cotta – low-fired clay, either glazed or unglazed.

Test cut – a sample of the roof system or assembly which exposes the roof deck and is used to diagnose the condition of the membrane, evaluate the type and number of plies or number of membranes, or rates of application (e.g., the weight of the average interply bitumen moppings).

Thatch Roof – the covering of a roof usually made of straw, reed, or natural foliage (palms) bound together to shed water.

Therm – a unit of heat equivalent to 100,000 BTUs (105.6 x 106). Commonly used by utilities in quoting prices or costs.

Thermal Barrier – a material applied over polyurethane foam designed to slow the temperature rise of the foam during a fire and delay its involvement in the fire. Thermal barriers for use with SPF must have a time rating of not less than 15 minutes.

Thermal block – a compression-resistant insulation block installed between structural steel and the panels and their supporting members to help maintain insulation R-values and reduce condensation.

Thermal bridge – the penetration of a material of high thermal conductivity (e.g., a metal insulation or roof membrane fastener) through a material of low thermal conductivity (e.g., thermal insulation); the result is a lowered thermal resistance for the assembly.

Thermal conductivity (k) – the time rate of heat flow through a unit area of a homogeneous material in a direction perpendicular to isothermal planes induced by a unit temperature gradient is called thermal conductivity (k or k-value). In English (inch-pound) units of measurement, it is the number of BTUs that pass through a 1 inch (25 mm) thickness of a 1 square foot (0.09 m2) sample of material in one hour with a temperature difference between the two surfaces of 1 degree F. In English (inch-pound) units it is expressed as Btu.inch/h.ft2.degree F. Note 1: A thermal conductivity (k) value applies to 1 inch (25 mm) thickness of a specific material. Note 2: It is mathematically incorrect to add, multiply, or divide the thermal conductivity (k) value of a material to determine the thermal performance value of a different thickness of the same material. If it is necessary to determine the thermal performance of a specific thickness of a material, it is appropriate to convert the thermal conductivity (k) of the material to a thermal resistance (R) value (i.e., R = 1/k), and then perform the mathematical calculation.

Thermal cycling – sequence of values by a repetitive temperature differential due to changes in radiant energy.

Thermal expansion – the increase in the dimension or volume of a body due to temperature variations.

Thermal Image – a visual representation of temperature distribution over a surface area. The image is displayed on a screen, presenting the response to infrared light waves.

Thermal insulation – A material designed to reduce the conductive heat flow.

Thermal movement – changes in dimension of a material as a result of temperature changes.

Thermal resistance (R) – under steady conditions, thermal resistance is the mean temperature difference between two defined surfaces of material or construction that induces unit heat flow through a unit area. In English (inch.pound) units it is expressed as degree F.ft2.h/Btu. Note 1: A thermal resistance (R) value applies to a specific thickness of a material or construction. Note 2: The thermal resistance (R) of a material is the reciprocal of the thermal conductance (C) of the same material (i.e., R = 1/C). Note 3: Thermal resistance (R) values can be added, subtracted, multiplied, and divided by mathematically appropriate methods.

Thermal shock – the stress-producing phenomenon resulting from sudden temperature changes in a roof membrane when, for example, a cold rain shower follows brilliant sunshine.

Thermal stress – stress introduced by uniform or non-uniform temperature change in a structure or material that is contained against expansion or contraction.

Thermal transmittance (U or U-factor) – thermal transmittance (U or U-factor) is the time rate of heat flow per unit area under steady conditions from the fluid (e.g., air) on the warm side of a barrier to the fluid (e.g., air) on the cold side, per unit temperature difference between the fluids. In English (inch.pound) units expressed as Btu/h.ft2.degree F. Note 1: A thermal temperature transmittance (U) value applies to the overall thermal performance of a system (e.g., roof assembly). Note 2: Thermal transmittance (U) is sometimes called the overall coefficient of heat transfer. Note 3: Thermal transmittance (U) is reciprocal of the overall thermal resistance (RT) of a system (i.e., U = 1/RT).

Thermogram – A visible light record of the display of an infrared camera system via a Polaroid print, 35 mm film, video tape, or a computer generated image.

Thermography – A technique for producing heat pictures from the invisible radiant energy emitted from stationary or moving objects at any distance and without in any way influencing the temperature of the objects under view. The electronic generation and display of a visible image of an infrared spectrum.

Thermoplastic – Capable of being repeatedly softened by increase of temperature and hardened by decrease in temperature. The thermoplastic form allows for easier seaming both in the factory and in the field.

Thermoplastic olefin membrane (TPO) – a blend of polypropylene and ethylene-propylene polymers. Colorant, flame retardants, UV absorbers, and other proprietary substances which may be blended with the TPO to achieve the desired physical properties. The membrane may or may not be reinforced.

Thermoplastic elastomers – Polymers capable of remelt, but exhibiting elastomeric properties; related to elasticized polyolefins. They have a limited upper temperature service range.

Thermoplastic resin – A material with a linear macromolecular structure that will repeatedly soften when heated and harden when cooled.

Thermoset – A material that will undergo (or has undergone) a chemical reaction by the action of heat, catalysts, ultraviolet light, etc., leading to a relatively infusible state.

Through-wall flashing – A water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct any water within the wall to the exterior.

Tensile test – A test in which a specimen is subjected to increasing longitudinal pulling stress until fracture occurs.

Therm – A unit of heat commonly used by utilities, equivalent to 100,000 BTU = 1.05 x 108 joules.

Thermal block – A spacer of low thermal conductance material, designed to prevent formation of a thermal bridge.

Thermal bridge – Interruption of a layer of thermal insulation by a material of high thermal conductivity (e.g. metal).

Thermal conductance (C) – The rate of heat flow through a material whose surfaces have stated a temperature differential Btu•in./h•ft40F(W/m2•0C).

Thermal conductivity (k) – The rate of heat flow

Thinner – (1) a volatile liquid added to an adhesive or coating material to modify the consistency or other properties; (2) a liquid used to clean equipment or other surfaces.

Thixotropic – the property of a material that enables it to stiffen in a relatively short time on standing, but6 upon agitation or manipulation to change to a very soft consistency or to a fluid of high viscosity, the process being completely reversible.

Thread Count – the number of threads per inch in each direction, with the warp mentioned first, and the fill second, (e.g., a thread count of 20 x 10 means 20 threads per inch [25.4mm] in the warp and 10 threads per inch [25.4mm] in the fill direction).

Through-wall flashing – a water-resistant membrane or material assembly extending totally through a wall and its cavities, positioned to direct water within the wall to the exterior, usually through weep holes.

Tie-in – in roofing and waterproofing, the transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings or by forming a watertight seal with the substrate, membrane, or adjacent roofing or waterproofing system.

Tie-Off – (in roofing and waterproofing) the transitional seal used to terminate a roofing or waterproofing application at the top or bottom of flashings, or by forming a watertight seal with the substrate, membrane or adjacent roofing or waterproofing system.

TIMA – Thermal Insulation Manufacturers Association

Toggle bolt – a bolt having a nut with pivoted, flanged wings that close against a spring when it is pushed through a hole, and open after emerging from the hole; used to fasten objects to a hollow wall or to a wall which is accessible only from one side.

Tongue and groove planks – one of the oldest types of dimensional structural wood used as roof decking. The sides are cut with convex and concave grooves so adjacent planks may join in alignment with each other to form a uniform roof deck.

Torch-applied – method used in the installation of polymer modified bitumen membranes characterized by using open flame propane torch equipment.

TPA – Tri-Polymer Alloy.

TPO – thermoplastic olefin.

Traffic bearing – in waterproofing, a membrane formulated to withstand a predetermined amount of pedestrian or vehicular traffic with separate protection and a wear course.

Transverse seam – the joint between the top of one metal roof panel and the bottom of the next panel, which runs perpendicular to the roof slope.

Treebark surface texture – in SPF roofing, the surface condition of the foam which shows a coarse texture where valleys form sharp angles. This surface is unacceptable for proper coating and protection.

Trim—The light gauge metal used in the finish of a building, especially around openings and at intersections of surfaces. Often referred to as flashing.

Tuckpointing – the process of removing deteriorated mortar from an existing masonry joint and troweling new mortar or other filler into the joint.

Two-Part System – a coating of SPF formed by the mixing and (usually) the reaction of two different materials.

U-Factor—The heat flow across an entire assembly e.g., from air within a building to outside air; the inverse of R-Factor.

U-value – see Thermal transmittance.

UBC – Uniform Building Code.

UL – Underwriters Laboratories, Inc.

UL label – an identification label or seal affixed to a roofing product or package with the authorization of Underwriters Laboratories, Inc. The presence of the label indicates that the product has met certain performance criteria.

Ultimate elongation—The elongation of a stretched specimen at the time of break. Usually reported as percent of the original length. Also called breaking strain.

Ultraviolet (UV) – invisible light radiation, adjacent to the violet end of the visible spectrum, with wavelengths from about 200 to 400 nm (nanometres).

Underlayment – an asphalt-saturated felt or other sheet material (may be self-adhering) installed between the roof deck and the roof covering, usually used in a steep-slope roof construction. Underlayment is primarily used to separate the roof covering from the roof deck, to shed water and to provide secondary weather protection for the roof area of the building.

Underwriters Laboratories, Inc. (UL) – an organization that tests, rates and classifies roof assemblies for their resistance to fire, impact, leakage, corrosion of metal components and wind uplift.

Uplift – see Wind uplift.

Unsupported sheeting—A polymer sheeting one or more plies thick without a reinforcing fabric layer or scrim.

Uplift—Wind load on a building, which causes a load in the upward direction. (See Suction)

Valley – the internal angle formed by the intersection of two sloping roof planes.

Valley gutter—A channel used to carry off water at the intersection of two sloping roof planes.

Vapor barrier—See Vapor Retarder.

Vapor migration—The flow of water vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor pressure—the pressure exerted by a vapor from a region of high vapor pressure to a region of lower vapor pressure.

Vapor retarder—a layer(s) of material or a laminate used to appreciably reduce the flow of water vapor into a roof assembly.

Vent—Opening designed to convey water vapor or other gas from inside a building or a building component to the atmosphere.

Ventilation Short Circuit-(as it relates to a passive ventilation system where the system is designed for air flow between intake and exhaust vents) a ventilation short circuit occurs when air is introduced into the ventilation system from an area higher than the intake vent thereby minimizing or defeating the effectiveness of the intake vent. One example can be a gable vent in a soffit-to-ridge ventilation system. Air intake from the gable vent can short circuit the stack-effect draw of air through the soffit vents, and interrupt the thorough venting of the roof cavity.

Ventilator—An accessory usually used on the roof that allows air to pass through.

Verge of popcorn texture – in SPF roofing, the verge of popcorn surface texture is the roughest texture suitable for receiving the protective coating on a sprayed polyurethane foam roof. The surface is acceptable for receiving a protective coating only because of the relatively cured valleys. However, the surface is considered undesirable because of the additional amount of coating material required to protect the surface properly.

Vermiculite—An aggregate used in lightweight insulating concrete, formed by heating and expanding a micaceous mineral.

Viscoelastic—Characterized by changing mechanical behavior, from nearly elastic at low temperature to plastic, like a viscous fluid, at high temperature.

Viscosity—Index of a fluid’s internal resistance to flow, measures in centistokes (cSt) for bitumens. (Water has a viscosity of roughly 1 cSt, light cooking oil 100 cSt.)

Viscosity – the resistance of a material to flow under stress. For bitumen, measured in centipoise. (see Viscous.)

Viscous – resistant to flow under stress.

Vulcanization—An irreversible process during which a rubber compound, through a change in its chemical structure, e.g., cross-linking, becomes less plastic and more resistant to swelling by organic liquids, and elastic proper- ties are conferred, improved, or extended over a greater range of temperature.

Warp—In textiles, the lengthwise yarns in a woven fabric.

Warm roof assembly – a roof assembly configured with each component placed immediately on top of the preceding component; each component is in contact with the adjacent component. No space is provided for ventilation of the roof assembly. Also known as a “compact” roof assembly.

Wash coat – a primer, typically provided on the back side of painted metal products to help protect the underlying metal from wear and corrosion.

Water Absorption – the amount of water absorbed by a material after immersion for a prescribed period of time. May be expressed as a percentage of the original weight of the material.

Water cure – a method of curing a material, such as concrete, by applying a fine mist of water over the surface to control the rate of moisture evaporation from the material.

Water cutoff – see Cutoff.

Waterproof – the quality of a membrane, membrane material, or other component to prevent water entry.

Waterproofing—Treatment of a surface or structure to prevent the passage of water under hydrostatic pressure.

Water-shedding – the ability of individual, overlapping components to resist the passage of water without hydrostatic pressure.

Water stop – a diaphragm used across a joint as a sealant, usually to prevent the passage of water.

Water table – the level within the ground, below which the soil is saturated with water.

Water vapor transmission – a measure of the rate of transmission of water vapor through a material under controlled laboratory conditions of temperature and humidity. Customary units are grains/hòft2.

Wear course – the top layer of surfacing that carries pedestrian or vehicular traffic. Sometimes referred to as wearing surface.

Wearing surface – see Wear course.

Weather Infiltration – the negative condition where rain or snow penetrate the roof. The condition is typically wind-driven.

Weatherometer—An instrument used to subject specimens to accelerated weathering conditions, e.g., rich UV source and water spray.

Weatherproof – the ability of a membrane or roof covering to prevent the passage of water with a limited amount of hydrostatic pressure.

Weep holes – small openings whose purpose is to permit drainage of water that accumulates inside a building component (e.g., a brick wall, skylight frame, etc.).

Weld – to join pieces of metal together by heat fusion.

Wet – a condition where free water is present in a substance.

Wet bulb temperature – the temperature of air as registered by a thermometer whose bulb is covered by a water wetted wick.

Wet film thickness – the thickness, expressed in mils, of a coating or mastic as applied but not cured. For comparison, see Dry film thickness.

Wicking—The process of moisture movement by capillary action as contrasted to movement of water vapor.

Wind clip – a steep-slope roofing attachment device that fits over the butt end of tile, slate and stone to help secure individual roofing units from wind uplift.

Wind load – force exerted by the wind on a structure or part of a structure.

Wind uplift – the force caused by the deflection of wind at roof edges, roof peaks or obstructions, causing a drop in air pressure immediately above the roof surface.

Windward – being in or facing the direction toward which the wind is blowing. The side exposed to the prevailing wind.

Wire Tie System – a scheme of attachment for steep-slope roofing units (e.g., tile, slate, and stone) utilizing fasteners (nails and/or screws) in conjunction with wire to make up a concealed fastening system.

Work slab – see Mud slab.

Woven valley – a method of valley construction in which shingles or roofing from both sides of the valley extend across the valley and are woven together by overlapping alternate courses as they are applied.

Wythe – a masonry wall, one masonry unit, a minimum of two inches thick.

Yield – in SPF-based roofing, the volume of foam per unit weight, normally expressed as board feet per pound or board feet per 1000 pounds.

Yield strength—(1) The longitudinal stress a material can bear before plastic deformation (i.e., elongation under constant stress); (2) The stress at which a material exhibits a specified reduction in the constant stress/strain ratio is the elastic range.

Yield strength—The stress at which a material exhibits a specified deviation from proportionality of stress and strain.

Z section – a member formed in the shape of a “Z” from coiled steel stock.

Zinc – a hard blush white metal, brittle at normal temperatures, very malleable and ductile when heated; not subject to corrosion; used for galvanizing sheet steel and iron, in various metal alloys, and as an oxide for white paint pigment.